emacs / etc / =news.texi

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
@setfilename LNEWS

@section New Features in the Lisp Language

@end itemize
@itemize @bullet
@item
The new function @code{delete} is a traditional Lisp function.  It takes
two arguments, @var{elt} and @var{list}, and deletes from @var{list} any
elements that are equal to @var{elt}.  It uses the function @code{equal}
to compare elements with @var{elt}.

@item
The new function @code{member} is a traditional Lisp function.  It takes
two arguments, @var{elt} and @var{list}, and finds the first element of
@var{list} that is equal to @var{elt}.  It uses the function
@code{equal} to compare each list element with @var{elt}.

The value is a sublist of @var{list}, whose first element is the one
that was found.  If no matching element is found, the value is
@code{nil}.

@ignore @c Seems not to be true, from looking at the code.
@item
The function @code{equal} is now more robust: it does not crash due to
circular list structure.
@end ignore

@item
The new function @code{indirect-function} finds the effective function
definition of an object called as a function.  If the object is a
symbol, @code{indirect-function} looks in the function definition of the
symbol.  It keeps doing this until it finds something that is not a
symbol.

@item
There are new escape sequences for use in character and string
constants.  The escape sequence @samp{\a} is equivalent to @samp{\C-g},
the @sc{ASCII} @sc{BEL} character (code 7).  The escape sequence
@samp{\x} followed by a hexidecimal number represents the character
whose @sc{ASCII} code is that number.  There is no limit on the number
of digits in the hexidecimal value.

@item
The function @code{read} when reading from a buffer now does not skip a
terminator character that terminates a symbol.  It leaves that character
to be read (or just skipped, if it is whitespace) next time.

@item
When you use a function @var{function} as the input stream for
@code{read}, it is usually called with no arguments, and should return
the next character.  In Emacs 19, sometimes @var{function} is called
with one argument (always a character).  When that happens,
@var{function} should save the argument and arrange to return it when
called next time.

@item
@code{random} with integer argument @var{n} returns a random number
between 0 and @var{n}@minus{}1.

@item
The functions @code{documentation} and @code{documentation-property} now
take an additional optional argument which, if non-@code{nil}, says to
refrain from calling @code{substitute-command-keys}.  This way, you get
the exact text of the documentation string as written, without the usual
substitutions.  Make sure to call @code{substitute-command-keys}
yourself if you decide to display the string.

@ignore
@item
The new function @code{invocation-name} returns as a string the program
name that was used to run Emacs, with any directory names discarded.
@c ??? This hasn't been written yet. ???
@end ignore

@item
The new function @code{map-y-or-n-p} makes it convenient to ask a series
of similar questions.  The arguments are @var{prompter}, @var{actor},
@var{list}, and optional @var{help}.

The value of @var{list} is a list of objects, or a function of no
arguments to return either the next object or @code{nil} meaning there
are no more.

The argument @var{prompter} specifies how to ask each question.  If
@var{prompter} is a string, the question text is computed like this:

@example
(format @var{prompter} @var{object})
@end example

@noindent
where @var{object} is the next object to ask about.

If not a string, @var{prompter} should be a function of one argument
(the next object to ask about) and should return the question text.

The argument @var{actor} should be a function of one argument, which is
called with each object that the user says yes for.  Its argument is
always one object from @var{list}.

If @var{help} is given, it is a list @code{(@var{object} @var{objects}
@var{action})}, where @var{object} is a string containing a singular
noun that describes the objects conceptually being acted on;
@var{objects} is the corresponding plural noun and @var{action} is a
transitive verb describing @var{actor}.  The default is @code{("object"
"objects" "act on")}.

Each time a question is asked, the user may enter @kbd{y}, @kbd{Y}, or
@key{SPC} to act on that object; @kbd{n}, @kbd{N}, or @key{DEL} to skip
that object; @kbd{!} to act on all following objects; @key{ESC} or
@kbd{q} to exit (skip all following objects); @kbd{.} (period) to act on
the current object and then exit; or @kbd{C-h} to get help.

@code{map-y-or-n-p} returns the number of objects acted on.

@item
You can now ``set'' environment variables with the @code{setenv}
command.  This works by setting the variable @code{process-environment},
which @code{getenv} now examines in preference to the environment Emacs
received from its parent.
@end itemize

@section New Features for Loading Libraries

You can now arrange to run a hook if a particular Lisp library is
loaded.

The variable @code{after-load-alist} is an alist of expressions to be
evalled when particular files are loaded.  Each element looks like
@code{(@var{filename} @var{forms}@dots{})}.

When @code{load} is run and the file name argument equals
@var{filename}, the @var{forms} in the corresponding element are
executed at the end of loading.  @var{filename} must match exactly!
Normally @var{filename} is the name of a library, with no directory
specified, since that is how @code{load} is normally called.

An error in @var{forms} does not undo the load, but does prevent
execution of the rest of the @var{forms}.

The function @code{eval-after-load} provides a convenient way to add
entries to the alist.  Call it with two arguments, @var{file} and a
form to execute.

The function @code{autoload} now supports autoloading a keymap.
Use @code{keymap} as the fourth argument if the autoloaded function
will become a keymap when loaded.

There is a new feature for specifying which functions in a library should
be autoloaded by writing special ``magic'' comments in that library itself.

  Write @samp{;;;###autoload} on a line by itself before a function
definition before the real definition of the function, in its
autoloadable source file; then the command @kbd{M-x
update-file-autoloads} automatically puts the @code{autoload} call into
@file{loaddefs.el}.

  You can also put other kinds of forms into @file{loaddefs.el}, by
writing @samp{;;;###autoload} followed on the same line by the form.
@kbd{M-x update-file-autoloads} copies the form from that line.

@section Compilation Features

@itemize @bullet
@item
Inline functions.

You can define an @dfn{inline function} with @code{defsubst}.  Use
@code{defsubst} just like @code{defun}, and it defines a function which
you can call in all the usual ways.  Whenever the function thus defined
is used in compiled code, the compiler will open code it.

You can get somewhat the same effects with a macro, but a macro has the
limitation that you can use it only explicitly; a macro cannot be called
with @code{apply}, @code{mapcar} and so on.  Also, it takes some work to
convert an ordinary function into a macro.  To convert it into an inline
function, simply replace @code{defun} with @code{defsubst}.

Making a function inline makes explicit calls run faster.  But it also
has disadvantages.  For one thing, it reduces flexibility; if you change
the definition of the function, calls already inlined still use the old
definition until you recompile them.

Another disadvantage is that making a large function inline can increase
the size of compiled code both in files and in memory.  Since the
advantages of inline functions are greatest for small functions, you
generally should not make large functions inline.

Inline functions can be used and open coded later on in the same file,
following the definition, just like macros.

@item
The command @code{byte-compile-file} now offers to save any buffer
visiting the file you are compiling.

@item
The new command @code{compile-defun} reads, compiles and executes the
defun containing point.  If you use this on a defun that is actually a
function definition, the effect is to install a compiled version of
that function.

@item
Whenever you load a Lisp file or library, you now receive a warning if
the directory contains both a @samp{.el} file and a @samp{.elc} file,
and the @samp{.el} file is newer.  This typically indicates that someone
has updated the Lisp code but forgotten to recompile it, so the changes
do not take effect.  The warning is a reminder to recompile.

@item
The special form @code{eval-when-compile} marks the forms it contains to
be evaluated at compile time @emph{only}.  At top-level, this is
analogous to the Common Lisp idiom @code{(eval-when (compile)
@dots{})}.  Elsewhere, it is similar to the Common Lisp @samp{#.} reader
macro (but not when interpreting).

If you're thinking of using this feature, we recommend you consider whether
@code{provide} and @code{require} might do the job as well.

@item
The special form @code{eval-and-compile} is similar to
@code{eval-when-compile}, but the whole form is evaluated both at
compile time and at run time.

If you're thinking of using this feature, we recommend you consider
whether @code{provide} and @code{require} might do the job as well.

@item
Emacs Lisp has a new data type for byte-code functions.  This makes
them faster to call, and also saves space.  Internally, a byte-code
function object is much like a vector; however, the evaluator handles
this data type specially when it appears as a function to be called.

The printed representation for a byte-code function object is like that
for a vector, except that it starts with @samp{#} before the opening
@samp{[}.  A byte-code function object must have at least four elements;
there is no maximum number, but only the first six elements are actually
used.  They are:

@table @var
@item arglist
The list of argument symbols.

@item byte-code
The string containing the byte-code instructions.

@item constants
The vector of constants referenced by the byte code.

@item stacksize
The maximum stack size this function needs.

@item docstring
The documentation string (if any); otherwise, @code{nil}.

@item interactive
The interactive spec (if any).  This can be a string or a Lisp
expression.  It is @code{nil} for a function that isn't interactive.
@end table

The predicate @code{byte-code-function-p} tests whether a given object
is a byte-code function.

You can create a byte-code function object in a Lisp program
with the function @code{make-byte-code}.  Its arguments are the elements
to put in the byte-code function object.

You should not try to come up with the elements for a byte-code function
yourself, because if they are inconsistent, Emacs may crash when you
call the function.  Always leave it to the byte compiler to create these
objects; it, we hope, always makes the elements consistent.
@end itemize

@section Floating Point Numbers

You can now use floating point numbers in Emacs, if you define the macro
@code{LISP_FLOAT_TYPE} when you compile Emacs.

The printed representation for floating point numbers requires either a
decimal point surrounded by digits, or an exponent, or both.  For
example, @samp{1500.0}, @samp{15e2}, @samp{15.0e2} and @samp{1.5e3} are
four ways of writing a floating point number whose value is 1500.

The existing predicate @code{numberp} now returns @code{t} if the
argument is any kind of number---either integer or floating.  The new
predicates @code{integerp} and @code{floatp} check for specific types of
numbers.

You can do arithmetic on floating point numbers with the ordinary
arithmetic functions, @code{+}, @code{-}, @code{*} and @code{/}.  If you
call one of these functions with both integers and floating point
numbers among the arguments, the arithmetic is done in floating point.
The same applies to the numeric comparison functions such as @code{=}
and @code{<}.  The remainder function @code{%} does not accept floating
point arguments, and neither do the bitwise boolean operations such as
@code{logand} or the shift functions such as @code{ash}.

There is a new arithmetic function, @code{abs}, which returns the absolute
value of its argument.  It handles both integers and floating point
numbers.

To convert an integer to floating point, use the function @code{float}.
There are four functions to convert floating point numbers to integers;
they differ in how they round.  @code{truncate} rounds toward 0,
@code{floor} rounds down, @code{ceil} rounds up, and @code{round}
produces the nearest integer.

You can use @code{logb} to extract the binary exponent of a floating
point number.  More precisely, it is the logarithm base 2, rounded down
to an integer.

Emacs has several new mathematical functions that accept any kind of
number as argument, but always return floating point numbers.

@table @code
@item cos
@findex cos
@itemx sin
@findex sin
@itemx tan
@findex tan
Trigonometric functions.
@item acos
@findex acos
@itemx asin
@findex asin
@itemx atan
@findex atan
Inverse trigonometric functions.
@item exp
@findex exp
The exponential function (power of @var{e}).
@item log
@findex log
Logarithm base @var{e}.
@item expm1
@findex expm1
Power of @var{e}, minus 1.
@item log1p
@findex log1p
Add 1, then take the logarithm.
@item log10
@findex log10
Logarithm base 10
@item expt
@findex expt
Raise @var{x} to power @var{y}.
@item sqrt
@findex sqrt
The square root function.
@end table

The new function @code{string-to-number} now parses a string containing
either an integer or a floating point number, returning the number.

The @code{format} function now handles the specifications @samp{%e},
@samp{%f} and @samp{%g} for printing floating point numbers; likewise
@code{message}.

The new variable @code{float-output-format} controls how Lisp prints
floating point numbers.  Its value should be @code{nil} or a string.

If it is a string, it should contain a @samp{%}-spec like those accepted
by @code{printf} in C, but with some restrictions.  It must start with
the two characters @samp{%.}.  After that comes an integer which is the
precision specification, and then a letter which controls the format.

The letters allowed are @samp{e}, @samp{f} and @samp{g}.  Use @samp{e}
for exponential notation (@samp{@var{dig}.@var{digits}e@var{expt}}).
Use @samp{f} for decimal point notation
(@samp{@var{digits}.@var{digits}}).  Use @samp{g} to choose the shorter
of those two formats for the number at hand.

The precision in any of these cases is the number of digits following
the decimal point.  With @samp{f}, a precision of 0 means to omit the
decimal point.  0 is not allowed with @samp{f} or @samp{g}.

A value of @code{nil} means to use the format @samp{%.20g}.

No matter what the value of @code{float-output-format}, printing ensures
that the result fits the syntax rules for a floating point number.  If
it doesn't fit (for example, if it looks like an integer), it is
modified to fit.  By contrast, the @code{format} function formats
floating point numbers without requiring the output to fit the
syntax rules for floating point number.

@section New Features for Printing And Formatting Output

@itemize @bullet
@item
The @code{format} function has a new feature: @samp{%S}.  This print
spec prints any kind of Lisp object, even a string, using its Lisp
printed representation.

By contrast, @samp{%s} prints everything without quotation.

@item
@code{prin1-to-string} now takes an optional second argument which says
not to print the Lisp quotation characters.  (In other words, to use
@code{princ} instead of @code{prin1}.)

@item
The new variable @code{print-level} specifies the maximum depth of list
nesting to print before cutting off all deeper structure.  A value of
@code{nil} means no limit.
@end itemize

@section Changes in Basic Editing Functions

@itemize @bullet
@item
There are two new primitives for putting text in the kill ring:
@code{kill-new} and @code{kill-append}.

The function @code{kill-new} adds a string to the front of the kill ring.

Use @code{kill-append} to add a string to a previous kill.  The second
argument @var{before-p}, if non-@code{nil}, says to add the string at
the beginning; otherwise, it goes at the end.

Both of these functions apply @code{interprogram-cut-function} to the
entire string of killed text that ends up at the beginning of the kill
ring.

@item
The new function @code{current-kill} rotates the yanking pointer in the
kill ring by @var{n} places, and returns the text at that place in the
ring.  If the optional second argument @var{do-not-move} is
non-@code{nil}, it doesn't actually move the yanking point; it just
returns the @var{n}th kill forward.  If @var{n} is zero, indicating a
request for the latest kill, @code{current-kill} calls
@code{interprogram-paste-function} (documented below) before consulting
the kill ring.

All Emacs Lisp programs should either use @code{current-kill},
@code{kill-new}, and @code{kill-append} to manipulate the kill ring, or
be sure to call @code{interprogram-paste-function} and
@code{interprogram-cut-function} as appropriate.

@item
The variables @code{interprogram-paste-function} and
@code{interprogram-cut-function} exist so that you can provide functions
to transfer killed text to and from other programs.

@item
The @code{kill-region} function can now be used in read-only buffers.
It beeps, but adds the region to the kill ring without deleting it.

@item
The new function @code{compare-buffer-substrings} lets you compare two
substrings of the same buffer or two different buffers.  Its arguments
look like this:

@example
(compare-buffer-substrings @var{buf1} @var{beg1} @var{end1} @var{buf2} @var{beg2} @var{end2})
@end example

The first three arguments specify one substring, giving a buffer and two
positions within the buffer.  The last three arguments specify the other
substring in the same way.

The value is negative if the first substring is less, positive if the
first is greater, and zero if they are equal.  The absolute value of
the result is one plus the index of the first different characters.

@item
Overwrite mode treats tab and newline characters specially.  You can now
turn off this special treatment by setting @code{overwrite-binary-mode}
to @code{t}.

@item
Once the mark ``exists'' in a buffer, it normally never ceases to
exist.  However, it may become @dfn{inactive}.  The variable
@code{mark-active}, which is always local in all buffers, indicates
whether the mark is active: non-@code{nil} means yes.

A command can request deactivation of the mark upon return to the editor
command loop by setting @code{deactivate-mark} to a non-@code{nil}
value.  Transient Mark mode works by causing the buffer modification
primitives to set @code{deactivate-mark}.

The variables @code{activate-mark-hook} and @code{deactivate-mark-hook}
are normal hooks run, respectively, when the mark becomes active andwhen
it becomes inactive.  The hook @code{activate-mark-hook} is also run at
the end of a command if the mark is active and the region may have
changed.

@item
The function @code{move-to-column} now accepts a second optional
argument @var{force}, in addition to @var{column}; if the requested
column @var{column} is in the middle of a tab character and @var{force}
is non-@code{nil}, @code{move-to-column} replaces the tab with the
appropriate sequence of spaces so that it can place point exactly at
@var{column}.

@item
The search functions when successful now return the value of point
rather than just @code{t}.  This affects the functions
@code{search-forward}, @code{search-backward},
@code{word-search-forward}, @code{word-search-backward},
@code{re-search-forward}, and @code{re-search-backward}.

@item
When you do regular expression searching or matching, there is no longer
a limit to how many @samp{\(@dots{}\)} pairs you can get information
about with @code{match-beginning} and @code{match-end}.  Also, these
parenthetical groupings may now be nested to any degree.

@item
The new special form @code{save-match-data} preserves the regular
expression match status.  Usage: @code{(save-match-data
@var{body}@dots{})}.

@item
The function @code{translate-region} applies a translation table to the
characters in a part of the buffer.  Invoke it as
@code{(translate-region @var{start} @var{end} @var{table})}; @var{start}
and @var{end} bound the region to translate.

The translation table @var{table} is a string; @code{(aref @var{table}
@var{ochar})} gives the translated character corresponding to
@var{ochar}.  If the length of @var{table} is less than 256, any
characters with codes larger than the length of @var{table} are not
altered by the translation.

@code{translate-region} returns the number of characters which were
actually changed by the translation.  This does not count characters
which were mapped into themselves in the translation table.

@item
There are two new hook variables that let you notice all changes in all
buffers (or in a particular buffer, if you make them buffer-local):
@code{before-change-function} and @code{after-change-function}.

If @code{before-change-function} is non-@code{nil}, then it is called
before any buffer modification.  Its arguments are the beginning and end
of the region that is going to change, represented as integers.  The
buffer that's about to change is always the current buffer.

If @code{after-change-function} is non-@code{nil}, then it is called
after any buffer modification.  It takes three arguments: the beginning
and end of the region just changed, and the length of the text that
existed before the change.  (To get the current length, subtract the
rrgion beginning from the region end.)  All three arguments are
integers.  The buffer that's about to change is always the current
buffer.

Both of these variables are temporarily bound to @code{nil} during the
time that either of these hooks is running.  This means that if one of
these functions changes the buffer, that change won't run these
functions.  If you do want hooks to be run recursively, write your hook
functions to bind these variables back to their usual values.

@item
The hook @code{first-change-hook} is run using @code{run-hooks} whenever
a buffer is changed that was previously in the unmodified state.

@item
The second argument to @code{insert-abbrev-table-description} is
now optional.
@end itemize

@section Text Properties

  Each character in a buffer or a string can have a @dfn{text property
list}, much like the property list of a symbol.  The properties belong
to a particular character at a particular place, such as, the letter
@samp{T} at the beginning of this sentence.  Each property has a name,
which is usually a symbol, and an associated value, which can be any
Lisp object---just as for properties of symbols (@pxref{Property Lists}).

  You can use the property @code{face-code} to control the font and
color of text.  That is the only property name which currently has a
special meaning, but you can create properties of any name and examine
them later for your own purposes.

  Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
@code{substring}, @code{insert}, and @code{buffer-substring}.

  Since text properties are considered part of the buffer contents,
changing properties in a buffer ``modifies'' the buffer, and you can
also undo such changes.

  Strings with text properties have a special printed representation
which describes all the properties.  This representation is also the
read syntax for such a string.  It looks like this:

@example
#("@var{characters}" @var{property-data}...)
@end example

@noindent
where @var{property-data} is zero or more elements in groups of three as
follows:

@example
@var{beg} @var{end} @var{plist}
@end example

@noindent
The elements @var{beg} and @var{end} are integers, and together specify
a portion of the string; @var{plist} is the property list for that
portion.

@subsection Examining Text Properties

  The simplest way to examine text properties is to ask for the value of
a particular property of a particular character.  For that, use
@code{get-text-property}.  Use @code{text-properties-at} to get the
entire property list of a character.  @xref{Property Search}, for
functions to examine the properties of a number of characters at once.

@code{(get-text-property @var{pos} @var{prop} @var{object})} returns the
@var{prop} property of the character after @var{pos} in @var{object} (a
buffer or string).  The argument @var{object} is optional and defaults
to the current buffer.

@code{(text-properties-at @var{pos} @var{object})} returns the entire
property list of the character after @var{pos} in the string or buffer
@var{object} (which defaults to the current buffer).

@subsection Changing Text Properties

  There are three primitives for changing properties of a specified
range of text:

@table @code
@item add-text-properties
This function puts on specified properties, leaving other existing
properties unaltered.

@item put-text-property
This function puts on a single specified property, leaving others
unaltered.

@item remove-text-properties
This function removes specified properties, leaving other
properties unaltered.

@item set-text-properties
This function replaces the entire property list, leaving no vessage of
the properties that that text used to have.
@end table

All these functions take four arguments: @var{start}, @var{end},
@var{props}, and @var{object}.  The last argument is optional and
defaults to the current buffer.  The argument @var{props} has the form
of a property list.

@subsection Property Search Functions

In typical use of text properties, most of the time several or many
consecutive characters have the same value for a property.  Rather than
writing your programs to examine characters one by one, it is much
faster to process chunks of text that have the same property value.

The functions @code{next-property-change} and
@code{previous-property-change} scan forward or backward from position
@var{pos} in @var{object}, looking for a change in any property between
two characters scanned.  They returns the position between those two
characters, or @code{nil} if no change is found.

The functions @code{next-single-property-change} and
@code{previous-single-property-change} are similar except that you
specify a particular property and they look for changes in the value of
that property only.  The property is the second argument, and
@var{object} is third.

@subsection Special Properties

  If a character has a @code{category} property, we call it the
@dfn{category} of the character.  It should be a symbol.  The properties
of the symbol serve as defaults for the properties of the character.

  You can use the property @code{face-code} to control the font and
color of text.  That is the only property name which currently has a
special meaning, but you can create properties of any name and examine
them later for your own purposes.
about face codes.

  You can specify a different keymap for a portion of the text by means
of a @code{local-map} property.  The property's value, for the character
after point, replaces the buffer's local map.

  If a character has the property @code{read-only}, then modifying that
character is not allowed.  Any command that would do so gets an error.

  If a character has the property @code{modification-hooks}, then its
value should be a list of functions; modifying that character calls all
of those functions.  Each function receives two arguments: the beginning
and end of the part of the buffer being modified.  Note that if a
particular modification hook function appears on several characters
being modified by a single primitive, you can't predict how many times
the function will be called.

  Insertion of text does not, strictly speaking, change any existing
character, so there is a special rule for insertion.  It compares the
@code{read-only} properties of the two surrounding characters; if they
are @code{eq}, then the insertion is not allowed.  Assuming insertion is
allowed, it then gets the @code{modification-hooks} properties of those
characters and calls all the functions in each of them.  (If a function
appears on both characters, it may be called once or twice.)

  The special properties @code{point-entered} and @code{point-left}
record hook functions that report motion of point.  Each time point
moves, Emacs compares these two property values:

@itemize @bullet
@item
the @code{point-left} property of the character after the old location,
and
@item
the @code{point-entered} property of the character after the new
location.
@end itemize

@noindent
If these two values differ, each of them is called (if not @code{nil})
with two arguments: the old value of point, and the new one.

  The same comparison is made for the characters before the old and new
locations.  The result may be to execute two @code{point-left} functions
(which may be the same function) and/or two @code{point-entered}
functions (which may be the same function).  The @code{point-left}
functions are always called before the @code{point-entered} functions.

  A primitive function may examine characters at various positions
without moving point to those positions.  Only an actual change in the
value of point runs these hook functions.

@section New Features for Files

@itemize @bullet
@item
The new function @code{file-accessible-directory-p} tells you whether
you can open files in a particular directory.  Specify as an argument
either a directory name or a file name which names a directory file.
The function returns @code{t} if you can open existing files in that
directory.

@item
The new function @code{file-executable-p} returns @code{t} if its
argument is the name of a file you have permission to execute.

@item
The function @code{file-truename} returns the ``true name'' of a
specified file.  This is the name that you get by following symbolic
links until none remain.  The argument must be an absolute file name.

@item
New functions @code{make-directory} and @code{delete-directory} create and
delete directories.  They both take one argument, which is the name of
the directory as a file.

@item
The function @code{read-file-name} now takes an additional argument
which specifies an initial file name.  If you specify this argument,
@code{read-file-name} inserts it along with the directory name.  It puts
the cursor between the directory and the initial file name.

The user can then use the initial file name unchanged, modify it, or
simply kill it with @kbd{C-k}.

If the variable @code{insert-default-directory} is @code{nil}, then the
default directory is not inserted, and the new argument is ignored.

@item
The function @code{file-relative-name} does the inverse of
expansion---it tries to return a relative name which is equivalent to
@var{filename} when interpreted relative to @var{directory}.  (If such a
relative name would be longer than the absolute name, it returns the
absolute name instead.)

@item
The function @code{file-newest-backup} returns the name of the most
recent backup file for @var{filename}, or @code{nil} that file has no
backup files.

@item
The list returned by @code{file-attributes} now has 12 elements.  The
12th element is the file system number of the file system that the file
is in.  This element together with the file's inode number, which is the
11th element, give enough information to distinguish any two files on
the system---no two files can have the same values for both of these
numbers.

@item
The new function @code{set-visited-file-modtime} updates the current
buffer's recorded modification time from the visited file's time.

This is useful if the buffer was not read from the file normally, or
if the file itself has been changed for some known benign reason.

If you give the function an argument, that argument specifies the new
value for the recorded modification time.  The argument should be a list
of the form @code{(@var{high} . @var{low})} or @code{(@var{high}
@var{low})} containing two integers, each of which holds 16 bits of the
time.  (This is the same format that @code[file-attributes} uses to
return time values.)

The new function @code{visited-file-modtime} returns the recorded last
modification time, in that same format.

@item
The function @code{directory-files} now takes an optional fourth
argument which, if non-@code{nil}, inhibits sorting the file names.
Use this if you want the utmost possible speed and don't care what order
the files are processed in.

If the order of processing is at all visible to the user, then the user
will probably be happier if you do sort the names.

@item
The variable @code{directory-abbrev-alist} contains an alist of
abbreviations to use for file directories.  Each element has the form
@code{(@var{from} . @var{to})}, and says to replace @var{from} with
@var{to} when it appears in a directory name.  This replacement is done
when setting up the default directory of a newly visited file.  The
@var{from} string is actually a regular expression; it should always
start with @samp{^}.

You can set this variable in @file{site-init.el} to describe the
abbreviations appropriate for your site.

@item
The function @code{abbreviate-file-name} applies abbreviations from
@code{directory-abbrev-alist} to its argument, and substitutes @samp{~}
for the user's home directory.

Abbreviated directory names are useful for directories that are normally
accessed through symbolic links.  If you think of the link's name as
``the name'' of the directory, you can define it as an abbreviation for
the directory's official name; then ordinarily Emacs will call that
directory by the link name you normally use.

@item
@code{write-region} can write a given string instead of text from the
buffer.  Use the string as the first argument (in place of the
starting character position).

You can supply a second file name as the fifth argument (@var{visit}).
Use this to write the data to one file (the first argument,
@var{filename}) while nominally visiting a different file (the fifth
argument, @var{visit}).  The argument @var{visit} is used in the echo
area message and also for file locking; @var{visit} is stored in
@code{buffer-file-name}.

@item
The value of @code{write-file-hooks} does not change when you switch to
a new major mode.  The intention is that these hooks have to do with
where the file came from, and not with what it contains.

@item
There is a new hook variable for saving files:
@code{write-contents-hooks}.  It works just like @code{write-file-hooks}
except that switching to a new major mode clears it back to @code{nil}.
Major modes should use this hook variable rather than
@code{write-file-hooks}.

@item
The hook @code{after-save-hook} runs just after a buffer has been saved
in its visited file.

@item
The new function @code{set-default-file-modes} sets the file protection
for new files created with Emacs.  The argument must be an integer.  (It
would be better to permit symbolic arguments like the @code{chmod}
program, but that would take more work than this function merits.)

Use the new function @code{default-file-modes} to read the current
default file mode.

@item
Call the new function @code{unix-sync} to force all pending disk output
to happen as soon as possible.
@end itemize

@section Making Certain File Names ``Magic''

You can implement special handling for a class of file names.  You must
supply a regular expression to define the class of names (all those
which match the regular expression), plus a handler that implements all
the primitive Emacs file operations for file names that do match.

The value of @code{file-name-handler-alist} is a list of handlers,
together with regular expressions that decide when to apply each
handler.  Each element has the form @code{(@var{regexp}
. @var{handler})}.  If a file name matches @var{regexp}, then all work
on that file is done by calling @var{handler}.

All the Emacs primitives for file access and file name transformation
check the given file name against @code{file-name-handler-alist}, and
call @var{handler} to do the work if appropriate.  The first argument
given to @var{handler} is the name of the primitive; the remaining
arguments are the arguments that were passed to that primitive.  (The
first of these arguments is typically the file name itself.)  For
example, if you do this:

@example
(file-exists-p @var{filename})
@end example

@noindent
and @var{filename} has handler @var{handler}, then @var{handler} is
called like this:

@example
(funcall @var{handler} 'file-exists-p @var{filename})
@end example

Here are the primitives that you can handle in this way:

@quotation
@code{add-name-to-file}, @code{copy-file}, @code{delete-directory},
@code{delete-file}, @code{directory-file-name}, @code{directory-files},
@code{dired-compress-file}, @code{dired-uncache},
@code{expand-file-name}, @code{file-accessible-directory-p},
@code{file-attributes}, @code{file-directory-p},
@code{file-executable-p}, @code{file-exists-p}, @code{file-local-copy},
@code{file-modes}, @code{file-name-all-completions},
@code{file-name-as-directory}, @code{file-name-completion},
@code{file-name-directory}, @code{file-name-nondirectory},
@code{file-name-sans-versions}, @code{file-newer-than-file-p},
@code{file-readable-p}, @code{file-symlink-p}, @code{file-writable-p},
@code{insert-directory}, @code{insert-file-contents},
@code{make-directory}, @code{make-symbolic-link}, @code{rename-file},
@code{set-file-modes}, @code{verify-visited-file-modtime},
@code{write-region}.
@end quotation

The handler function must handle all of the above operations, and
possibly others to be added in the future.  Therefore, it should always
reinvoke the ordinary Lisp primitive when it receives an operation it
does not recognize.  Here's one way to do this:

@smallexample
(defun my-file-handler (primitive &rest args)
  ;; @r{First check for the specific operations}
  ;; @r{that we have special handling for.}
  (cond ((eq operation 'insert-file-contents) @dots{})
        ((eq operation 'write-region) @dots{})
        @dots{}
        ;; @r{Handle any operation we don't know about.}
        (t (let (file-name-handler-alist)
             (apply operation args)))))
@end smallexample

The function @code{file-local-copy} copies file @var{filename} to the
local site, if it isn't there already.  If @var{filename} specifies a
``magic'' file name which programs outside Emacs cannot directly read or
write, this copies the contents to an ordinary file and returns that
file's name.

If @var{filename} is an ordinary file name, not magic, then this function
does nothing and returns @code{nil}.

The function @code{unhandled-file-name-directory} is used to get a
non-magic directory name from an arbitrary file name.  It uses the
directory part of the specified file name if that is not magic.
Otherwise, it asks the file name's handler what to do.

@section Frames
@cindex frame

Emacs now supports multiple X windows via a new data type known as a
@dfn{frame}.

A frame is a rectangle on the screen that contains one or more Emacs
windows.  Subdividing a frame works just like subdividing the screen in
earlier versions of Emacs.

@cindex terminal frame
There are two kinds of frames: terminal frames and X window frames.
Emacs creates one terminal frame when it starts up with no X display; it
uses Termcap or Terminfo to display using characters.  There is no way
to create another terminal frame after startup.  If Emacs has an X
display, it does not make a terminal frame, and there is none.

@cindex X window frame
When you are using X windows, Emacs starts out with a single X window
frame.  You can create any number of X window frames using
@code{make-frame}.

Use the predicate @code{framep} to determine whether a given Lisp object
is a frame.

The function @code{redraw-frame} redisplays the entire contents of a
given frame.

@subsection Creating and Deleting Frames

Use @code{make-frame} to create a new frame (supported under X Windows
only).  This is the only primitive for creating frames.

@code{make-frame} takes just one argument, which is an alist
specifying frame parameters.  Any parameters not mentioned in the
argument alist default based on the value of @code{default-frame-alist};
parameters not specified there default from the standard X defaults file
and X resources.

When you invoke Emacs, if you specify arguments for window appearance
and so forth, these go into @code{default-frame-alist} and that is how
they have their effect.

You can specify the parameters for the initial startup X window frame by
setting @code{initial-frame-alist} in your @file{.emacs} file.  If these
parameters specify a separate minibuffer-only frame, and you have not
created one, Emacs creates one for you, using the parameter values
specified in @code{minibuffer-frame-alist}.

You can specify the size and position of a frame using the frame
parameters @code{left}, @code{top}, @code{height} and @code{width}.  You
must specify either both size parameters or neither.  You must specify
either both position parameters or neither.  The geometry parameters
that you don't specify are chosen by the window manager in its usual
fashion.

The function @code{x-parse-geometry} converts a standard X windows
geometry string to an alist which you can use as part of the argument to
@code{make-frame}.

Use the function @code{delete-frame} to eliminate a frame.  Frames are
like buffers where deletion is concerned; a frame actually continues to
exist as a Lisp object until it is deleted @emph{and} there are no
references to it, but once it is deleted, it has no further effect on
the screen.

The function @code{frame-live-p} returns non-@code{nil} if the argument
(a frame) has not been deleted.

@subsection Finding All Frames

The function @code{frame-list} returns a list of all the frames that have
not been deleted.  It is analogous to @code{buffer-list}.  The list that
you get is newly created, so modifying the list doesn't have any effect
on the internals of Emacs.  The function @code{visible-frame-list} returns
the list of just the frames that are visible.

@code{next-frame} lets you cycle conveniently through all the frames from an
arbitrary starting point.  Its first argument is a frame.  Its second
argument @var{minibuf} says what to do about minibuffers:

@table @asis
@item @code{nil}
Exclude minibuffer-only frames.
@item a window
Consider only the frames using that particular window as their
minibuffer.
@item anything else
Consider all frames.
@end table

@subsection Frames and Windows

All the non-minibuffer windows in a frame are arranged in a tree of
subdivisions; the root of this tree is available via the function
@code{frame-root-window}.  Each window is part of one and only one
frame; you can get the frame with @code{window-frame}.

At any time, exactly one window on any frame is @dfn{selected within the
frame}.  You can get the frame's current selected window with
@code{frame-selected-window}.  The significance of this designation is
that selecting the frame selects for Emacs as a whole the window
currently selected within that frame.

Conversely, selecting a window for Emacs with @code{select-window} also
makes that window selected within its frame.

@subsection Frame Visibility

A frame may be @dfn{visible}, @dfn{invisible}, or @dfn{iconified}.  If
it is invisible, it doesn't show in the screen, not even as an icon.
You can set the visibility status of a frame with
@code{make-frame-visible}, @code{make-frame-invisible}, and
@code{iconify-frame}.  You can examine the visibility status with
@code{frame-visible-p}---it returns @code{t} for a visible frame,
@code{nil} for an invisible frame, and @code{icon} for an iconified
frame.

@subsection Selected Frame

At any time, one frame in Emacs is the @dfn{selected frame}.  The selected
window always resides on the selected frame.

@defun selected-frame
This function returns the selected frame.
@end defun

The X server normally directs keyboard input to the X window that the
mouse is in.  Some window managers use mouse clicks or keyboard events
to @dfn{shift the focus} to various X windows, overriding the normal
behavior of the server.

Lisp programs can switch frames ``temporarily'' by calling the function
@code{select-frame}.  This does not override the window manager; rather,
it escapes from the window manager's control until that control is
somehow reasserted.  The function takes one argument, a frame, and
selects that frame.  The selection lasts until the next time the user
does something to select a different frame, or until the next time this
function is called.

Emacs cooperates with the X server and the window managers by arranging
to select frames according to what the server and window manager ask
for.  It does so by generating a special kind of input event, called a
@dfn{focus} event.  The command loop handles a focus event by calling
@code{internal-select-frame}.  @xref{Focus Events}.

@subsection Frame Size and Position

The new functions @code{frame-height} and @code{frame-width} return the
height and width of a specified frame (or of the selected frame),
measured in characters.

The new functions @code{frame-pixel-height} and @code{frame-pixel-width}
return the height and width of a specified frame (or of the selected
frame), measured in pixels.

The new functions @code{frame-char-height} and @code{frame-char-width}
return the height and width of a character in a specified frame (or in
the selected frame), measured in pixels.

@code{set-frame-size} sets the size of a frame, measured in characters;
its arguments are @var{frame}, @var{cols} and @var{rows}.  To set the
size with values measured in pixels, you can use
@code{modify-frame-parameters}.

The function @code{set-frame-position} sets the position of the top left
corner of a frame.  Its arguments are @var{frame}, @var{left} and
@var{top}.

@ignore
New functions @code{set-frame-height} and @code{set-frame-width} set the
size of a specified frame.  The frame is the first argument; the size is
the second.
@end ignore

@subsection Frame Parameters

A frame has many parameters that affect how it displays.  Use the
function @code{frame-parameters} to get an alist of all the parameters
of a given frame.  To alter parameters, use
@code{modify-frame-parameters}, which takes two arguments: the frame to
modify, and an alist of parameters to change and their new values.  Each
element of @var{alist} has the form @code{(@var{parm} . @var{value})},
where @var{parm} is a symbol.  Parameters that aren't meaningful are
ignored.  If you don't mention a parameter in @var{alist}, its value
doesn't change.

Just what parameters a frame has depends on what display mechanism it
uses.  Here is a table of the parameters of an X
window frame:

@table @code
@item name
The name of the frame.

@item left
The screen position of the left edge.

@item top
The screen position of the top edge.

@item height
The height of the frame contents, in pixels.

@item width
The width of the frame contents, in pixels.

@item window-id
The number of the X window for the frame.

@item minibuffer
Whether this frame has its own minibuffer.
@code{t} means yes, @code{none} means no, 
@code{only} means this frame is just a minibuffer,
a minibuffer window (in some other frame)
means the new frame uses that minibuffer.

@item font
The name of the font for the text.

@item foreground-color
The color to use for the inside of a character.
Use strings to designate colors;
X windows defines the meaningful color names.

@item background-color
The color to use for the background of text.

@item mouse-color
The color for the mouse cursor.

@item cursor-color
The color for the cursor that shows point.

@item border-color
The color for the border of the frame.

@item cursor-type
The way to display the cursor.  There are two legitimate values:
@code{bar} and @code{box}.  The value @code{bar} specifies a vertical
bar between characters as the cursor.  The value @code{box} specifies an
ordinary black box overlaying the character after point; that is the
default.

@item icon-type
Non-@code{nil} for a bitmap icon, @code{nil} for a text icon.

@item border-width
The width in pixels of the window border.

@item internal-border-width
The distance in pixels between text and border.

@item auto-raise
Non-@code{nil} means selecting the frame raises it.

@item auto-lower
Non-@code{nil} means deselecting the frame lowers it.

@item vertical-scrollbar
Non-@code{nil} gives the frame a scroll bar
for vertical scrolling.

@item horizontal-scrollbar
Non-@code{nil} gives the frame a scroll bar
for horizontal scrolling.
@end table

@subsection Minibufferless Frames

Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected.  However, you can also create
frames with no minibuffers.  These frames must use the minibuffer window
of some other frame.

The variable @code{default-minibuffer-frame} specifies where to find a
minibuffer for frames created without minibuffers of their own.  Its
value should be a frame which does have a minibuffer.

You can also specify a minibuffer window explicitly when you create a
frame; then @code{default-minibuffer-frame} is not used.

@section X Windows Features

@itemize @bullet
@item
The new functions @code{mouse-position} and @code{set-mouse-position} give
access to the current position of the mouse.

@code{mouse-position} returns a description of the position of the mouse.
The value looks like @code{(@var{frame} @var{x} . @var{y})}, where @var{x}
and @var{y} are measured in pixels relative to the top left corner of
the inside of @var{frame}.

@code{set-mouse-position} takes three arguments, @var{frame}, @var{x}
and @var{y}, and warps the mouse cursor to that location on the screen.

@item
@code{track-mouse} is a new special form for tracking mouse motion.
Use it in definitions of mouse clicks that want pay to attention to
the motion of the mouse, not just where the buttons are pressed and
released.  Here is how to use it:

@example
(track-mouse @var{body}@dots{})
@end example

While @var{body} executes, mouse motion generates input events just as mouse
clicks do.  @var{body} can read them with @code{read-event} or
@code{read-key-sequence}.

@code{track-mouse} returns the value of the last form in @var{body}.

The format of these events is described under ``New features for key
bindings and input.''
@c ???

@item
@code{x-set-selection} sets a ``selection'' in the X Windows server.
It takes two arguments: a selection type @var{type}, and the value to
assign to it, @var{data}.  If @var{data} is @code{nil}, it means to
clear out the selection.  Otherwise, @var{data} may be a string, a
symbol, an integer (or a cons of two integers or list of two integers),
or a cons of two markers pointing to the same buffer.  In the last case,
the selection is considered to be the text between the markers.  The
data may also be a vector of valid non-vector selection values.

Each possible @var{type} has its own selection value, which changes
independently.  The usual values of @var{type} are @code{PRIMARY} and
@code{SECONDARY}; these are symbols with upper-case names, in accord
with X Windows conventions.  The default is @code{PRIMARY}.

To get the value of the selection, call @code{x-get-selection}.  This
function accesses selections set up by Emacs and those set up by other X
clients.  It takes two optional arguments, @var{type} and
@var{data-type}.  The default for @var{type} is @code{PRIMARY}.

The @var{data-type} argument specifies the form of data conversion to
use; meaningful values include @code{TEXT}, @code{STRING},
@code{TARGETS}, @code{LENGTH}, @code{DELETE}, @code{FILE_NAME},
@code{CHARACTER_POSITION}, @code{LINE_NUMBER}, @code{COLUMN_NUMBER},
@code{OWNER_OS}, @code{HOST_NAME}, @code{USER}, @code{CLASS},
@code{NAME}, @code{ATOM}, and @code{INTEGER}.  (These are symbols with
upper-case names in accord with X Windows conventions.)
The default for @var{data-type} is @code{STRING}.

@item
X Windows has a set of numbered @dfn{cut buffers} which can store text
or other data being moved between applications.  Use
@code{x-get-cut-buffer} to get the contents of a cut buffer; specify the
cut buffer number as argument.  Use @code{x-set-cut-buffer} with
argument @var{string} to store a new string into the first cut buffer
(moving the other values down through the series of cut buffers,
kill-ring-style).

Cut buffers are considered obsolete in X Windows, but Emacs supports
them for the sake of X clients that still use them.

@item
You can close the connection with the X Windows server with
the function @code{x-close-current-connection}.  This takes no arguments.

Then you can connect to a different X Windows server with
@code{x-open-connection}.  The first argument, @var{display}, is the
name of the display to connect to.

The optional second argument @var{xrm-string} is a string of resource
names and values, in the same format used in the @file{.Xresources}
file.  The values you specify override the resource values recorded in
the X Windows server itself.  Here's an example of what this string
might look like:

@example
"*BorderWidth: 3\n*InternalBorder: 2\n"
@end example

@item
A series of new functions give you information about the X server and
the screen you are using.

@table @code
@item x-display-screens
The number of screens associated with the current display.

@item x-server-version
The version numbers of the X server in use.

@item x-server-vendor
The vendor supporting the X server in use.

@item x-display-pixel-height
The height of this X screen in pixels.

@item x-display-mm-height
The height of this X screen in millimeters.

@item x-display-pixel-width
The width of this X screen in pixels.

@item x-display-mm-width
The width of this X screen in millimeters.

@item x-display-backing-store
The backing store capability of this screen.  Values can be the symbols
@code{always}, @code{when-mapped}, or @code{not-useful}.

@item x-display-save-under
Non-@code{nil} if this X screen supports the SaveUnder feature.

@item x-display-planes
The number of planes this display supports.

@item x-display-visual-class
The visual class for this X screen.  The value is one of the symbols
@code{static-gray}, @code{gray-scale}, @code{static-color},
@code{pseudo-color}, @code{true-color}, and @code{direct-color}.

@item x-display-color-p
@code{t} if the X screen in use is a color screen.

@item x-display-color-cells
The number of color cells this X screen supports.
@end table

There is also a variable @code{x-no-window-manager}, whose value is
@code{t} if no X window manager is in use.

@item
The function @code{x-synchronize} enables or disables an X Windows
debugging mode: synchronous communication.  It takes one argument,
non-@code{nil} to enable the mode and @code{nil} to disable.

In synchronous mode, Emacs waits for a response to each X protocol
command before doing anything else.  This means that errors are reported
right away, and you can directly find the erroneous command.
Synchronous mode is not the default because it is much slower.

@item
The function @code{x-get-resource} retrieves a resource value from the X
Windows defaults database.  Its three arguments are @var{attribute},
@var{name} and @var{class}.  It searches using a key of the form
@samp{@var{instance}.@var{attribute}}, with class @samp{Emacs}, where
@var{instance} is the name under which Emacs was invoked.

The optional arguments @var{component} and @var{subclass} add to the key
and the class, respectively.  You must specify both of them or neither.
If you specify them, the key is
@samp{@var{instance}.@var{component}.@var{attribute}}, and the class is
@samp{Emacs.@var{subclass}}.

@item
@code{x-color-display-p} returns @code{t} if you are using an X Window
server with a color display, and @code{nil} otherwise.

@c ??? Name being changed from x-defined-color.
@code{x-color-defined-p} takes as argument a string describing a color; it
returns @code{t} if the display supports that color.  (If the color is
@code{"black"} or @code{"white"} then even black-and-white displays
support it.)

@item
@code{x-popup-menu} has been generalized.  It now accepts a keymap as
the @var{menu} argument.  Then the menu items are the prompt strings of
individual key bindings, and the item values are the keys which have
those bindings.

You can also supply a list of keymaps as the first argument; then each
keymap makes one menu pane (but keymaps that don't provide any menu
items don't appear in the menu at all).

@code{x-popup-menu} also accepts a mouse button event as the
@var{position} argument.  Then it displays the menu at the location at
which the event took place.  This is convenient for mouse-invoked
commands that pop up menus.

@ignore
@item
x-pointer-shape, x-nontext-pointer-shape, x-mode-pointer-shape.
@end ignore

@item
You can use the function @code{x-rebind-key} to change the sequence
of characters generated by one of the keyboard keys.  This works
only with X Windows.

The first two arguments, @var{keycode} and @var{shift-mask}, should be
numbers representing the keyboard code and shift mask respectively.
They specify what key to change.

The third argument, @var{newstring}, is the new definition of the key.
It is a sequence of characters that the key should produce as input.

The shift mask value is a combination of bits according to this table:

@table @asis
@item 8
Control
@item 4
Meta
@item 2
Shift
@item 1
Shift Lock
@end table

If you specify @code{nil} for @var{shift-mask}, then the key specified
by @var{keycode} is redefined for all possible shift combinations.

For the possible values of @var{keycode} and their meanings, see the
file @file{/usr/lib/Xkeymap.txt}.  Keep in mind that the codes in that
file are in octal!

@ignore @c Presumably this is already fixed
NOTE: due to an X bug, this function will not take effect unless the
user has a @file{~/.Xkeymap} file.  (See the documentation for the
@code{keycomp} program.)  This problem will be fixed in X version 11.
@end ignore

The related function @code{x-rebind-keys} redefines a single keyboard
key, specifying the behavior for each of the 16 shift masks
independently.  The first argument is @var{keycode}, as in
@code{x-rebind-key}.  The second argument @var{strings} is a list of 16
elements, one for each possible shift mask value; each element says how
to redefine the key @var{keycode} with the corresponding shift mask
value.  If an element is a string, it is the new definition.  If an
element is @code{nil}, the definition does not change for that shift
mask.

@item
The function @code{x-geometry} parses a string specifying window size
and position in the usual fashion for X windows.  It returns an alist
describing which parameters were specified, and the values that were
given for them.

The elements of the alist look like @code{(@var{parameter} .
@var{value})}.  The possible @var{parameter} values are @code{left},
@code{top}, @code{width}, and @code{height}.
@end itemize

@section New Window Features

@itemize @bullet
@item
The new function @code{window-at} tells you which window contains a
given horizontal and vertical position on a specified frame.  Call it
with three arguments, like this:

@example
(window-at @var{x} @var{column} @var{frame})
@end example

The function returns the window which contains that cursor position in
the frame @var{frame}.  If you omit @var{frame}, the selected frame is
used.

@item
The function @code{coordinates-in-window-p} takes two arguments and
checks whether a particular frame position falls within a particular
window.

@example
(coordinates-in-window-p @var{coordinates} @var{window})
@end example

The argument @var{coordinates} is a cons cell of this form:

@example
(@var{x} . @var{y})
@end example

@noindent
The two coordinates are measured in characters, and count from the top
left corner of the screen or frame.

The value of the function tells you what part of the window the position
is in.  The possible values are:

@table @code
@item (@var{relx} . @var{rely})
The coordinates are inside @var{window}.  The numbers @var{relx} and
@var{rely} are equivalent window-relative coordinates, counting from 0
at the top left corner of the window.

@item mode-line
The coordinates are in the mode line of @var{window}.

@item vertical-split
The coordinates are in the vertical line between @var{window} and its
neighbor to the right.

@item nil
The coordinates are not in any sense within @var{window}.
@end table

You need not specify a frame when you call
@code{coordinates-in-window-p}, because it assumes you mean the frame
which window @var{window} is on.

@item
The function @code{minibuffer-window} now accepts a frame as argument
and returns the minibuffer window used for that frame.  If you don't
specify a frame, the currently selected frame is used.  The minibuffer
window may be on the frame in question, but if that frame has no
minibuffer of its own, it uses the minibuffer window of some other
frame, and @code{minibuffer-window} returns that window.

@item
Use @code{window-live-p} to test whether a window is still alive (that
is, not deleted).

@item
Use @code{window-minibuffer-p} to determine whether a given window is a
minibuffer or not.  It no longer works to do this by comparing the
window with the result of @code{(minibuffer-window)}, because there can
be more than one minibuffer window at a time (if you have multiple
frames).

@item
If you set the variable @code{pop-up-frames} non-@code{nil}, then the
functions to show something ``in another window'' actually create a new
frame for the new window.  Thus, you will tend to have a frame for each
window, and you can easily have a frame for each buffer.

The value of the variable @code{pop-up-frame-function} controls how new
frames are made.  The value should be a function which takes no
arguments and returns a frame.  The default value is a function which
creates a frame using parameters from @code{pop-up-frame-alist}.

@item
@code{display-buffer} is the basic primitive for finding a way to show a
buffer on the screen.  You can customize its behavior by storing a
function in the variable @code{display-buffer-function}.  If this
variable is non-@code{nil}, then @code{display-buffer} calls it to do
the work.  Your function should accept two arguments, as follows:

@table @var
@item buffer
The buffer to be displayed.

@item flag
A flag which, if non-@code{nil}, means you should find another window to
display @var{buffer} in, even if it is already visible in the selected
window.
@end table

The function you supply will be used by commands such as
@code{switch-to-buffer-other-window} and @code{find-file-other-window}
as well as for your own calls to @code{display-buffer}.

@item
@code{delete-window} now gives all of the deleted window's screen space
to a single neighboring window.  Likewise, @code{enlarge-window} takes
space from only one neighboring window until that window disappears;
only then does it take from another window.

@item
@code{next-window} and @code{previous-window} accept another argument,
@var{all-frames}.

These functions now take three optional arguments: @var{window},
@var{minibuf} and @var{all-frames}.  @var{window} is the window to start
from (@code{nil} means use the selected window).  @var{minibuf} says
whether to include the minibuffer in the windows to cycle through:
@code{t} means yes, @code{nil} means yes if it is active, and anything
else means no.

Normally, these functions cycle through all the windows in the
selected frame, plus the minibuffer used by the selected frame even if
it lies in some other frame.

If @var{all-frames} is @code{t}, then these functions cycle through
all the windows in all the frames that currently exist.  If
@var{all-frames} is neither @code{t} nor @code{nil}, then they limit
themselves strictly to the windows in the selected frame, excluding the
minibuffer in use if it lies in some other frame.

@item
The functions @code{get-lru-window} and @code{get-largest-window} now
take an optional argument @var{all-frames}.  If it is non-@code{nil},
the functions consider all windows on all frames.  Otherwise, they
consider just the windows on the selected frame.

Likewise, @code{get-buffer-window} takes an optional second argument
@var{all-frames}.

@item
The variable @code{other-window-scroll-buffer} specifies which buffer
@code{scroll-other-window} should scroll.

@item
You can now mark a window as ``dedicated'' to its buffer.
Then Emacs will not try to use that window for any other buffer
unless you explicitly request it.

Use the new function @code{set-window-dedicated-p} to set the dedication
flag of a window @var{window} to the value @var{flag}.  If @var{flag} is
@code{t}, this makes the window dedicated.  If @var{flag} is
@code{nil}, this makes the window non-dedicated.

Use @code{window-dedicated-p} to examine the dedication flag of a
specified window.

@item
The new function @code{walk-windows} cycles through all visible
windows, calling @code{proc} once for each window with the window as
its sole argument.

The optional second argument @var{minibuf} says whether to include minibuffer
windows.  A value of @code{t} means count the minibuffer window even if
not active.  A value of @code{nil} means count it only if active.  Any
other value means not to count the minibuffer even if it is active.

If the optional third argument @var{all-frames} is @code{t}, that means
include all windows in all frames.  If @var{all-frames} is @code{nil},
it means to cycle within the selected frame, but include the minibuffer
window (if @var{minibuf} says so) that that frame uses, even if it is on
another frame.  If @var{all-frames} is neither @code{nil} nor @code{t},
@code{walk-windows} sticks strictly to the selected frame.

@item
The function @code{window-end} is a counterpart to @code{window-start}:
it returns the buffer position of the end of the display in a given
window (or the selected window).

@item
The function @code{window-configuration-p} returns non-@code{nil} when
given an object that is a window configuration (such as is returned by
@code{current-window-configuration}).
@end itemize

@section Display Features

@itemize @bullet
@item
@samp{%l} as a mode line item displays the current line number.

If the buffer is longer than @code{line-number-display-limit}
characters, or if lines are too long in the viscinity of the current
displayed text, then line number display is inhibited to save time.

The default contents of the mode line include the line number if
@code{line-number-mode} is non-@code{nil}.

@item
@code{baud-rate} is now a variable rather than a function.  This is so
you can set it to reflect the effective speed of your terminal, when the
system doesn't accurately know the speed.

@item
You can now remove any echo area message and make the minibuffer
visible.  To do this, call @code{message} with @code{nil} as the only
argument.  This clears any existing message, and lets the current
minibuffer contents show through.  Previously, there was no reliable way
to make sure that the minibuffer contents were visible.

@item
The variable @code{temp-buffer-show-hook} has been renamed
@code{temp-buffer-show-function}, because its value is a single function
(of one argument), not a normal hook.

@item
The new function @code{force-mode-line-update} causes redisplay
of the current buffer's mode line.
@end itemize

@section Display Tables

@cindex display table
You can use the @dfn{display table} feature to control how all 256
possible character codes display on the screen.  This is useful for
displaying European languages that have letters not in the ASCII
character set.

The display table maps each character code into a sequence of
@dfn{glyphs}, each glyph being an image that takes up one character
position on the screen.  You can also define how to display each glyph
on your terminal, using the @dfn{glyph table}.

@subsection Display Tables

Use @code{make-display-table} to create a display table.  The table
initially has @code{nil} in all elements.

A display table is actually an array of 261 elements.  The first 256
elements of a display table control how to display each possible text
character.  The value should be @code{nil} or a vector (which is a
sequence of glyphs; see below).  @code{nil} as an element means to
display that character following the usual display conventions.

The remaining five elements of a display table serve special purposes
(@code{nil} means use the default stated below):

@table @asis
@item 256
The glyph for the end of a truncated screen line (the default for this
is @samp{\}).
@item 257
The glyph for the end of a continued line (the default is @samp{$}).
@item 258
The glyph for the indicating an octal character code (the default is
@samp{\}).
@item 259
The glyph for indicating a control characters (the default is @samp{^}).
@item 260
The vector of glyphs for indicating the presence of invisible lines (the
default is @samp{...}).
@end table

Each buffer typically has its own display table.  The display table for
the current buffer is stored in @code{buffer-display-table}.  (This
variable automatically becomes local if you set it.)  If this variable
is @code{nil}, the value of @code{standard-display-table} is used in
that buffer.

Each window can have its own display table, which overrides the display
table of the buffer it is showing.

If neither the selected window nor the current buffer has a display
table, and if @code{standard-display-table} is @code{nil}, then Emacs
uses the usual display conventions:

@itemize @bullet
@item
Character codes 32 through 127 map to glyph codes 32 through 127.
@item
Codes 0 through 31 map to sequences of two glyphs, where the first glyph
is the ASCII code for @samp{^}.
@item
Character codes 128 through 255 map to sequences of four glyphs, where
the first glyph is the ASCII code for @samp{\}, and the others represent
digits.
@end itemize

The usual display conventions are also used for any character whose
entry in the active display table is @code{nil}.  This means that when
you set up a display table, you need not specify explicitly what to do
with each character, only the characters for which you want unusual
behavior.

@subsection Glyphs

@cindex glyph
A glyph stands for an image that takes up a single character position on
the screen.  A glyph is represented in Lisp as an integer.

@cindex glyph table
The meaning of each integer, as a glyph, is defined by the glyph table,
which is the value of the variable @code{glyph-table}.  It should be a
vector; the @var{g}th element defines glyph code @var{g}.  The possible
definitions of a glyph code are:

@table @var
@item integer
Define this glyph code as an alias for code @var{integer}.
This is used with X windows to specify a face code.

@item string
Send the characters in @var{string} to the terminal to output
this glyph.  This alternative is not available with X Windows.

@item @code{nil}
This glyph is simple.  On an ordinary terminal, the glyph code mod 256
is the character to output.  With X, the glyph code mod 256 is character
to output, and the glyph code divided by 256 specifies the @dfn{face
code} to use while outputting it.
@end table

Any glyph code beyond the length of the glyph table is automatically simple.

A face code for X windows is the combination of a font and a color.
Emacs uses integers to identify face codes.  You can define a new face
code with @code{(x-set-face @var{face-code} @var{font} @var{foreground}
@var{background})}.  @var{face-code} is an integer from 0 to 255; it
specifies which face to define.  The other three arguments are strings:
@var{font} is the name of the font to use, and @var{foreground} and
@var{background} specify the colors to use.

If @code{glyph-table} is @code{nil}, then all possible glyph codes are
simple.

@subsection ISO Latin 1

If you have a terminal that can handle the entire ISO Latin 1 character
set, you can arrange to use that character set as follows:

@example
(require 'disp-table)
(standard-display-8bit 0 255)
@end example

If you are editing buffers written in the ISO Latin 1 character set and
your terminal doesn't handle anything but ASCII, you can load the file
@code{iso-ascii} to set up a display table which makes the other ISO
characters display as sequences of ASCII characters.  For example, the
character ``o with umlaut'' displays as @samp{@{"o@}}.

Some European countries have terminals that don't support ISO Latin 1
but do support the special characters for that country's language.  You
can define a display table to work one language using such terminals.
For an example, see @file{lisp/iso-swed.el}, which handles certain
Swedish terminals.

You can load the appropriate display table for your terminal
automatically by writing a terminal-specific Lisp file for the terminal
type.

@section New Input Event Formats

Mouse clicks, mouse movements and function keys no longer appear in the
input stream as characters; instead, other kinds of Lisp objects
represent them as input.

@itemize @bullet
@item
An ordinary input character event consists of a @dfn{basic code} between
0 and 255, plus any or all of these @dfn{modifier bits}:

@table @asis
@item meta
The 2**23 bit in the character code indicates a character
typed with the meta key held down.

@item control
The 2**22 bit in the character code indicates a non-@sc{ASCII}
control character.

@sc{ASCII} control characters such as @kbd{C-a} have special basic
codes of their own, so Emacs needs no special bit to indicate them.
Thus, the code for @kbd{C-a} is just 1.

But if you type a control combination not in @sc{ASCII}, such as
@kbd{%} with the control key, the numeric value you get is the code
for @kbd{%} plus 2**22 (assuming the terminal supports non-@sc{ASCII}
control characters).

@item shift
The 2**21 bit in the character code indicates an @sc{ASCII} control
character typed with the shift key held down.

For letters, the basic code indicates upper versus lower case; for
digits and punctuation, the shift key selects an entirely different
character with a different basic code.  In order to keep within
the @sc{ASCII} character set whenever possible, Emacs avoids using
the 2**21 bit for those characters.

However, @sc{ASCII} provides no way to distinguish @kbd{C-A} from
@kbd{C-A}, so Emacs uses the 2**21 bit in @kbd{C-A} and not in
@kbd{C-a}.

@item hyper
The 2**20 bit in the character code indicates a character
typed with the hyper key held down.

@item super
The 2**19 bit in the character code indicates a character
typed with the super key held down.

@item alt
The 2**18 bit in the character code indicates a character typed with
the alt key held down.  (On some terminals, the key labeled @key{ALT}
is actually the meta key.)
@end table

In the future, Emacs may support a larger range of basic codes.  We may
also move the modifier bits to larger bit numbers.  Therefore, you
should avoid mentioning specific bit numbers in your program.  Instead,
the way to test the modifier bits of a character is with the function
@code{event-modifiers} (see below).

@item
Function keys are represented as symbols.  The symbol's name is
the function key's label.  For example, pressing a key labeled @key{F1}
places the symbol @code{f1} in the input stream.

There are a few exceptions to the symbol naming convention:

@table @asis
@item @code{kp-add}, @code{kp-decimal}, @code{kp-divide}, @dots{}
Keypad keys (to the right of the regular keyboard).
@item @code{kp-0}, @code{kp-1}, @dots{}
Keypad keys with digits.
@item @code{kp-f1}, @code{kp-f2}, @code{kp-f3}, @code{kp-f4}
Keypad PF keys.
@item @code{left}, @code{up}, @code{right}, @code{down}
Cursor arrow keys
@end table

You can use the modifier keys @key{CTRL}, @key{META}, @key{HYPER},
@key{SUPER}, @key{ALT} and @key{SHIFT} with function keys.  The way
to represent them is with prefixes in the symbol name:

@table @samp
@item A-
The alt modifier.
@item C-
The control modifier.
@item H-
The hyper modifier.
@item M-
The meta modifier.
@item s-
The super modifier.
@item S-
The shift modifier.
@end table

Thus, the symbol for the key @key{F3} with @key{META} held down is
kbd{M-@key{F3}}.  When you use more than one prefix, we recommend you
write them in alphabetical order (though the order does not matter in
arguments to the key-binding lookup and modification functions).

@item
Mouse events are represented as lists.

If you press a mouse button and release it at the same location, this
generates a ``click'' event.  Mouse click events have this form:

@example
(@var{button-symbol}
 (@var{window} (@var{column} . @var{row})
  @var{buffer-pos} @var{timestamp}))
@end example

Here is what the elements normally mean:

@table @var
@item button-symbol
indicates which mouse button was used.  It is one of the symbols
@code{mouse-1}, @code{mouse-2}, @dots{}, where the buttons are numbered
numbered left to right.

You can also use prefixes @samp{A-}, @samp{C-}, @samp{H-}, @samp{M-},
@samp{S-} and @samp{s-} for modifiers alt, control, hyper, meta, shift
and super, just as you would with function keys.

@item window
is the window in which the click occurred.

@item column
@itemx row
are the column and row of the click, relative to the top left corner of
@var{window}, which is @code{(0 . 0)}.

@item buffer-pos
is the buffer position of the character clicked on.

@item timestamp
is the time at which the event occurred, in milliseconds.  (Since this
value wraps around the entire range of Emacs Lisp integers in about five
hours, it is useful only for relating the times of nearby events.)
@end table

The meanings of @var{buffer-pos}, @var{row} and @var{column} are
somewhat different when the event location is in a special part of the
screen, such as the mode line or a scroll bar.

If the position is in the window's scroll bar, then @var{buffer-pos} is
the symbol @code{vertical-scrollbar} or @code{horizontal-scrollbar}, and
the pair @code{(@var{column} . @var{row})} is instead a pair
@code{(@var{portion} . @var{whole})}, where @var{portion} is the
distance of the click from the top or left end of the scroll bar, and
@var{whole} is the length of the entire scroll bar.

If the position is on a mode line or the vertical line separating
@var{window} from its neighbor to the right, then @var{buffer-pos} is
the symbol @code{mode-line} or @code{vertical-line}.  In this case
@var{row} and @var{column} do not have meaningful data.

@item
Releasing a mouse button above a different character position
generates a ``drag'' event, which looks like this:

@example
(@var{button-symbol}
 (@var{window1} (@var{column1} . @var{row1})
  @var{buffer-pos1} @var{timestamp1})
 (@var{window2} (@var{column2} . @var{row2})
  @var{buffer-pos2} @var{timestamp2}))
@end example

The name of @var{button-symbol} contains the prefix @samp{drag-}.  The
second and third elements of the event give the starting and ending
position of the drag.

The @samp{drag-} prefix follows the modifier key prefixes such as
@samp{C-} and @samp{M-}.

If @code{read-key-sequence} receives a drag event which has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position.  This means that you don't have to distinguish between click
and drag events unless you want to.

@item
Click and drag events happen when you release a mouse button.  Another
kind of event happens when you press a button.  It looks just like a
click event, except that the name of @var{button-symbol} contains the
prefix @samp{down-}.  The @samp{down-} prefix follows the modifier key
prefixes such as @samp{C-} and @samp{M-}.

The function @code{read-key-sequence}, and the Emacs command loop,
ignore any down events that don't have command bindings.  This means
that you need not worry about defining down events unless you want them
to do something.  The usual reason to define a down event is so that you
can track mouse motion until the button is released.

@item
For example, if the user presses and releases the left mouse button over
the same location, Emacs generates a sequence of events like this:

@smallexample
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
(mouse-1      (#<window 18 on NEWS> 2613 (0 . 38) -864180))
@end smallexample

Or, while holding the control key down, the user might hold down the
second mouse button, and drag the mouse from one line to the next.
That produces two events, as shown here:

@smallexample
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
                (#<window 18 on NEWS> 3510 (0 . 28) -729648))
@end smallexample

Or, while holding down the meta and shift keys, the user might press
the second mouse button on the window's mode line, and then drag the
mouse into another window.  That produces an event like this:

@smallexample
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
                  (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
                   -453816))
@end smallexample

@item
A key sequence that starts with a mouse click is read using the keymaps
of the buffer in the window clicked on, not the current buffer.

This does not imply that clicking in a window selects that window or its
buffer.  The execution of the command begins with no change in the
selected window or current buffer.  However, the command can switch
windows or buffers if programmed to do so.

@item
Mouse motion events are represented by lists.  During the execution of
the body of a @code{track-mouse} form, moving the mouse generates events
that look like this:

@example
(mouse-movement (@var{window} (@var{column} . @var{row})
                 @var{buffer-pos} @var{timestamp}))
@end example

The second element of the list describes the current position of the
mouse, just as in a mouse click event.

Outside of @code{track-mouse} forms, Emacs does not generate events for
mere motion of the mouse, and these events do not appear.

@item
Focus shifts between frames are represented by lists.

When the mouse shifts temporary input focus from one frame to another,
Emacs generates an event like this:

@example
(switch-frame @var{new-frame})
@end example

@noindent
where @var{new-frame} is the frame switched to.

In X windows, most window managers are set up so that just moving the
mouse into a window is enough to set the focus there.  As far as the
user concern, Emacs behaves consistently with this.  However, there is
no need for the Lisp program to know about the focus change until some
other kind of input arrives.  So Emacs generates the focus event only
when the user actually types a keyboard key or presses a mouse button in
the new frame; just moving the mouse between frames does not generate a
focus event.

The global key map usually binds this event to the
@code{internal-select-frame} function, so that characters typed at a
frame apply to that frame's selected window.

If the user switches frames in the middle of a key sequence, then Emacs
delays the @code{switch-frame} event until the key sequence is over.
For example, suppose @kbd{C-c C-a} is a key sequence in the current
buffer's keymaps.  If the user types @kbd{C-c}, moves the mouse to
another frame, and then types @kbd{C-a}, @code{read-key-sequence}
returns the sequence @code{"\C-c\C-a"}, and the next call to
@code{read-event} or @code{read-key-sequence} will return the
@code{switch-frame} event.
@end itemize

@section Working with Input Events

@itemize @bullet
@item
Functions which work with key sequences now handle non-character
events.  Functions like @code{define-key}, @code{global-set-key}, and
@code{local-set-key} used to accept strings representing key sequences;
now, since events may be arbitrary lisp objects, they also accept
vectors.  The function @code{read-key-sequence} may return a string or a
vector, depending on whether or not the sequence read contains only
characters.

List events may be represented by the symbols at their head; to bind
clicks of the left mouse button, you need only present the symbol
@code{mouse-1}, not an entire mouse click event.  If you do put an event
which is a list in a key sequence, only the event's head symbol is used
in key lookups.

For example, to globally bind the left mouse button to the function
@code{mouse-set-point}, you could evaluate this:

@example
(global-set-key [mouse-1] 'mouse-set-point)
@end example

To bind the sequence @kbd{C-c @key{F1}} to the command @code{tex-view}
in @code{tex-mode-map}, you could evaluate this:

@example
(define-key tex-mode-map [?\C-c f1] 'tex-view)
@end example

To find the binding for the function key labeled @key{NEXT} in
@code{minibuffer-local-map}, you could evaluate this:

@example
(lookup-key minibuffer-local-map [next])
     @result{} next-history-element
@end example

If you call the function @code{read-key-sequence} and then press
@kbd{C-x C-@key{F5}}, here is how it behaves:

@example
(read-key-sequence "Press `C-x C-F5': ")
     @result{} [24 C-f5]
@end example

Note that @samp{24} is the character @kbd{C-x}.

@item
The documentation functions (@code{single-key-description},
@code{key-description}, etc.) now handle the new event types.  Wherever
a string of keyboard input characters was acceptable in previous
versions of Emacs, a vector of events should now work.

@item
Special parts of a window can have their own bindings for mouse events.

When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event itself shows nothing special---only the
symbol that would normally represent that mouse button and modifier
keys.  The information about the screen region is kept in other parts
of the event list.  But @code{read-key-sequence} translates this
information into imaginary prefix keys, all of which are symbols:
@code{mode-line}, @code{vertical-line}, @code{horizontal-scrollbar} and
@code{vertical-scrollbar}.

For example, if you call @code{read-key-sequence} and then click the
mouse on the window's mode line, this is what happens:

@smallexample
(read-key-sequence "Click on the mode line: ")
     @result{} [mode-line (mouse-1 (#<window 6 on NEWS> mode-line
                              (40 . 63) 5959987))]
@end smallexample

You can define meanings for mouse clicks in special window regions by
defining key sequences using these imaginary prefix keys.  For example,
here is how to bind the third mouse button on a window's mode line
delete the window:

@example
(global-set-key [mode-line mouse-3] 'mouse-delete-window)
@end example

Here's how to bind the middle button (modified by @key{META}) on the
vertical line at the right of a window to scroll the window to the
left.

@example
(global-set-key [vertical-line M-mouse-2] 'scroll-left)
@end example

@item
Decomposing an event symbol.

Each symbol used to identify a function key or mouse button has a
property named @code{event-symbol-elements}, which is a list containing
an unmodified version of the symbol, followed by modifiers the symbol
name contains.  The modifiers are symbols; they include @code{shift},
@code{control}, and @code{meta}.  In addition, a mouse event symbol has
one of @code{click}, @code{drag}, and @code{down}.  For example:

@example
(get 'f5 'event-symbol-elements)
     @result{} (f5)
(get 'C-f5 'event-symbol-elements)
     @result{} (f5 control)
(get 'M-S-f5 'event-symbol-elements)
     @result{} (f5 meta shift)
(get 'mouse-1 'event-symbol-elements)
     @result{} (mouse-1 click)
(get 'down-mouse-1 'event-symbol-elements)
     @result{} (mouse-1 down)
@end example

Note that the @code{event-symbol-elements} property for a mouse click
explicitly contains @code{click}, but the event symbol name itself does
not contain @samp{click}.

@item
Use @code{read-event} to read input if you want to accept any kind of
event.  The old function @code{read-char} now discards events other than
keyboard characters.

@item
@code{last-command-char} and @code{last-input-char} can now hold any
kind of event.

@item
The new variable @code{unread-command-events} is much like
@code{unread-command-char}.  Its value is a list of events of any type,
to be processed as command input in order of appearance in the list.

@item
The function @code{this-command-keys} may return a string or a vector,
depending on whether or not the sequence read contains only characters.
You may need to upgrade code which uses this function.

The function @code{recent-keys} now returns a vector of events.
You may need to upgrade code which uses this function.

@item
A keyboard macro's definition can now be either a string or a vector.
All that really matters is what elements it has.  If the elements are
all characters, then the macro can be a string; otherwise, it has to be
a vector.

@item
The variable @code{last-event-frame} records which frame the last input
event was directed to.  Usually this is the frame that was selected when
the event was generated, but if that frame has redirected input focus to
another frame, @code{last-event-frame} is the frame to which the event
was redirected.

@item
The interactive specification now allows a new code letter @samp{e} to
simplify commands bound to events which are lists.  This code supplies
as an argument the complete event object.

You can use @samp{e} more than once in a single command's interactive
specification.  If the key sequence which invoked the command has
@var{n} events with parameters, the @var{n}th @samp{e} provides the
@var{n}th parameterized event.  Events which are not lists, such as
function keys and ASCII keystrokes, do not count where @samp{e} is
concerned.

@item
You can extract the starting and ending position values from a mouse
button or motion event using the two functions @code{event-start} and
@code{event-end}.  These two functions return different values for drag
and motion events; for click and button-down events, they both return
the position of the event.

@item
The position, a returned by @code{event-start} and @code{event-end}, is
a list of this form:

@example
(@var{window} @var{buffer-position} (@var{col} . @var{row}) @var{timestamp})
@end example

You can extract parts of this list with the functions
@code{posn-window}, @code{posn-point}, @code{posn-col-row}, and
@code{posn-timestamp}.

@item
The function @code{scroll-bar-scale} is useful for computing where to
scroll to in response to a mouse button event from a scroll bar.  It
takes two arguments, @var{ratio} and @var{total}, and in effect
multiplies them.  We say ``in effect'' because @var{ratio} is not a
number; rather a pair @code{(@var{num} . @var{denom}).

Here's the usual way to use @code{scroll-bar-scale}:

@example
(scroll-bar-scale (posn-col-row (event-start event))
                  (buffer-size))
@end example
@end itemize

@section Putting Keyboard Events in Strings

  In most of the places where strings are used, we conceptualize the
string as containing text characters---the same kind of characters found
in buffers or files.  Occasionally Lisp programs use strings which
conceptually contain keyboard characters; for example, they may be key
sequences or keyboard macro definitions.  There are special rules for
how to put keyboard characters into a string, because they are not
limited to the range of 0 to 255 as text characters are.

  A keyboard character typed using the @key{META} key is called a
@dfn{meta character}.  The numeric code for such an event includes the
2**23 bit; it does not even come close to fitting in a string.  However,
earlier Emacs versions used a different representation for these
characters, which gave them codes in the range of 128 to 255.  That did
fit in a string, and many Lisp programs contain string constants that
use @samp{\M-} to express meta characters, especially as the argument to
@code{define-key} and similar functions.

  We provide backward compatibility to run those programs with special
rules for how to put a keyboard character event in a string.  Here are
the rules:

@itemize @bullet
@item
If the keyboard event value is in the range of 0 to 127, it can go in the
string unchanged.

@item
The meta variants of those events, with codes in the range of 2**23 to
2**23+127, can also go in the string, but you must change their numeric
values.  You must set the 2**7 bit instead of the 2**23 bit, resulting
in a value between 128 and 255.

@item
Other keyboard character events cannot fit in a string.  This includes
keyboard events in the range of 128 to 255.
@end itemize

  Functions such as @code{read-key-sequence} that can construct strings
containing events follow these rules.

  When you use the read syntax @samp{\M-} in a string, it produces a
code in the range of 128 to 255---the same code that you get if you
modify the corresponding keyboard event to put it in the string.  Thus,
meta events in strings work consistently regardless of how they get into
the strings.

  New programs can avoid dealing with these rules by using vectors
instead of strings for key sequences when there is any possibility that
these issues might arise.

  The reason we changed the representation of meta characters as
keyboard events is to make room for basic character codes beyond 127,
and support meta variants of such larger character codes.

@section Menus

You can now define menus conveniently as keymaps.  Menus are normally
used with the mouse, but they can work with the keyboard also.

@subsection Defining Menus

A keymap is suitable for menu use if it has an @dfn{overall prompt
string}, which is a string that appears as an element of the keymap.  It
should describes the purpose of the menu.  The easiest way to construct
a keymap with a prompt string is to specify the string as an argument
when you run @code{make-keymap} or @code{make-sparse-keymap}.

The individual bindings in the menu keymap should also have prompt
strings; these strings are the items in the menu.  A binding with a
prompt string looks like this:

@example
(@var{char} @var{string} . @var{real-binding})
@end example

As far as @code{define-key} is concerned, the string is part of the
character's binding---the binding looks like this:

@example
(@var{string} . @var{real-binding}).
@end example

However, only @var{real-binding} is used for executing the key.

You can also supply a second string, called the help string, as follows:

@example
(@var{char} @var{string} @var{help-string} . @var{real-binding})
@end example

Currently Emacs does not actually use @var{help-string}; it knows only
how to ignore @var{help-string} in order to extract @var{real-binding}.
In the future we hope to make @var{help-string} serve as longer
documentation for the menu item, available on request.

The prompt string for a binding should be short---one or two words.  Its
meaning should describe the command it corresponds to.

If @var{real-binding} is @code{nil}, then @var{string} appears in the
menu but cannot be selected.

If @var{real-binding} is a symbol, and has a non-@code{nil}
@code{menu-enable} property, that property is an expression which
controls whether the menu item is enabled.  Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-@code{nil}.  When a
menu item is disabled, it is displayed in a ``fuzzy'' fashion, and
cannot be selected with the mouse.

@subsection Menus and the Mouse

The way to make a menu keymap produce a menu is to make it the
definition of a prefix key.

When the prefix key ends with a mouse event, Emacs handles the menu
keymap by popping up a visible menu that you can select from with the
mouse.  When you click on a menu item, the event generated is whatever
character or symbol has the binding which brought about that menu item.

A single keymap can appear as multiple panes, if you explicitly
arrange for this.  The way to do this is to make a keymap for each
pane, then create a binding for each of those maps in the main keymap
of the menu.  Give each of these bindings a prompt string that starts
with @samp{@@}.  The rest of the prompt string becomes the name of the
pane.  See the file @file{lisp/mouse.el} for an example of this.  Any
ordinary bindings with prompt strings are grouped into one pane, which
appears along with the other panes explicitly created for the
submaps.

You can also get multiple panes from separate keymaps.  The full
definition of a prefix key always comes from merging the definitions
supplied by the various active keymaps (minor modes, local, and
global).  When more than one of these keymaps is a menu, each of them
makes a separate pane or panes.

@subsection Menus and the Keyboard

When a prefix key ending with a keyboard event (a character or function
key) has a definition that is a menu keymap, you can use the keyboard
to choose a menu item.

Emacs displays the menu alternatives in the echo area.  If they don't
all fit at once, type @key{SPC} to see the next line of alternatives.
If you keep typing @key{SPC}, you eventually get to the end of the menu
and then cycle around to the beginning again.

When you have found the alternative you want, type the corresponding
character---the one whose binding is that alternative.

In a menu intended for keyboard use, each menu item must clearly
indicate what character to type.  The best convention to use is to make
the character the first letter of the menu item prompt string.  That is
something users will understand without being told.

@subsection The Menu Bar

  Under X Windows, each frame can have a @dfn{menu bar}---a permanently
displayed menu stretching horizontally across the top of the frame.  The
items of the menu bar are the subcommands of the fake ``function key''
@code{menu-bar}, as defined by all the active keymaps.

  To add an item to the menu bar, invent a fake ``function key'' of your
own (let's call it @var{key}), and make a binding for the key sequence
@code{[menu-bar @var{key}]}.  Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.

  In order for a frame to display a menu bar, its @code{menu-bar-lines}
property must be greater than zero.  Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame.  We
recommend you try one or two as the @code{menu-bar-lines} value.

@section Keymaps

@itemize @bullet
@item
The representation of keymaps has changed to support the new event
types.  All keymaps now have the form @code{(keymap @var{element}
@var{element} @dots{})}.  Each @var{element} takes one of the following
forms:

@table @asis
@item @var{prompt-string}
A string as an element of the keymap marks the keymap as a menu, and
serves as the overal prompt string for it.

@item @code{(@var{key} . @var{binding})}
A cons cell binds @var{key} to @var{definition}.  Here @var{key} may be
any sort of event head---a character, a function key symbol, or a mouse
button symbol.

@item @var{vector}
A vector of 128 elements binds all the ASCII characters; the @var{n}th
element holds the binding for character number @var{n}.

@item @code{(t . @var{binding})}
A cons cell whose @sc{car} is @code{t} is a default binding; anything
not bound by previous keymap elements is given @var{binding} as its
binding.

Default bindings are important because they allow a keymap to bind all
possible events without having to enumerate all the possible function
keys and mouse clicks, with all possible modifier prefixes.

The function @code{lookup-key} (and likewise other functions for
examining a key binding) normally report only explicit bindings of the
specified key sequence; if there is none, they return @code{nil}, even
if there is a default binding that would apply to that key sequence if
it were actually typed in.  However, these functions now take an
optional argument @var{accept-defaults} which, if non-@code{nil}, says
to consider default bindings.

Note that if a vector in the keymap binds an ASCII character to
@code{nil} (thus making it ``unbound''), the default binding does not
apply to the character.  Think of the vector element as an explicit
binding of @code{nil}.

Note also that if the keymap for a minor or major mode contains a
default binding, it completely masks out any lower-priority keymaps.
@end table

@item
A keymap can now inherit from another keymap.  Do do this, make the
latter keymap the ``tail'' of the new one.  Such a keymap looks like
this:

@example
(keymap @var{bindings}@dots{} . @var{other-keymap})
@end example

The effect is that this keymap inherits all the bindings of
@var{other-keymap}, but can add to them or override them with
@var{bindings}.  Subsequent changes in the bindings of
@var{other-keymap} @emph{do} affect this keymap.

For example, 

@example
(setq my-mode-map (cons 'keymap text-mode-map))
@end example

@noindent
makes a keymap that by default inherits all the bindings of Text
mode---whatever they may be at the time a key is looked up.  Any
bindings made explicitly in @code{my-mode-map} override the bindings
inherited from Text mode, however.

@item
Minor modes can now have local keymaps.  Thus, a key can act a special
way when a minor mode is in effect, and then revert to the major mode or
global definition when the minor mode is no longer in effect.  The
precedence of keymaps is now: minor modes (in no particular order), then
major mode, and lastly the global map.

The new @code{current-minor-mode-maps} function returns a list of all
the keymaps of currently enabled minor modes, in the other that they
apply.

To set up a keymap for a minor mode, add an element to the alist
@code{minor-mode-map-alist}.  Its elements look like this:

@example
(@var{symbol} . @var{keymap})
@end example

The keymap @var{keymap} is active whenever @var{symbol} has a
non-@code{nil} value.  Use for @var{symbol} the variable which indicates
whether the minor mode is enabled.

When more than one minor mode keymap is active, their order of
precedence is the order of @code{minor-mode-map-alist}.  But you should
design minor modes so that they don't interfere with each other, and if
you do this properly, the order will not matter.

The function @code{minor-mode-key-binding} returns a list of all the
active minor mode bindings of @var{key}.  More precisely, it returns an
alist of pairs @code{(@var{modename} . @var{binding})}, where
@var{modename} is the the variable which enables the minor mode, and
@var{binding} is @var{key}'s definition in that mode.  If @var{key} has
no minor-mode bindings, the value is @code{nil}.

If the first binding is a non-prefix, all subsequent bindings from other
minor modes are omitted, since they would be completely shadowed.
Similarly, the list omits non-prefix bindings that follow prefix
bindings.

@item
The new function @code{copy-keymap} copies a keymap, producing a new
keymap with the same key bindings in it.  If the keymap contains other
keymaps directly, these subkeymaps are copied recursively.

If you want to, you can define a prefix key with a binding that is a
symbol whose function definition is another keymap.  In this case,
@code{copy-keymap} does not look past the symbol; it doesn't copy the
keymap inside the symbol.

@item
@code{substitute-key-definition} now accepts an optional fourth
argument, which is a keymap to use as a template.

@example
(substitute-key-definition olddef newdef keymap oldmap)
@end example

@noindent
finds all characters defined in @var{oldmap} as @var{olddef},
and defines them in @var{keymap} as @var{newdef}.

In addition, this function now operates recursively on the keymaps that
define prefix keys within @var{keymap} and @var{oldmap}.
@end itemize

@section Minibuffer Features

The minibuffer input functions @code{read-from-minibuffer} and
@code{completing-read} have new features.

@subsection Minibuffer History

A new optional argument @var{hist} specifies which history list to use.
If you specify a variable (a symbol), that variable is the history
list.  If you specify a cons cell @code{(@var{variable}
. @var{startpos})}, then @var{variable} is the history list variable,
and @var{startpos} specifies the initial history position (an integer,
counting from zero which specifies the most recent element of the
history).

If you specify @var{startpos}, then you should also specify that element
of the history as @var{initial-input}, for consistency.

If you don't specify @var{hist}, then the default history list
@code{minibuffer-history} is used.  Other standard history lists that
you can use when appropriate include @code{query-replace-history},
@code{command-history}, and @code{file-name-history}.

The value of the history list variable is a list of strings, most recent
first.  You should set a history list variable to @code{nil} before
using it for the first time.

@code{read-from-minibuffer} and @code{completing-read} add new elements
to the history list automatically, and provide commands to allow the
user to reuse items on the list.  The only thing your program needs to
do to use a history list is to initialize it and to pass its name to the
input functions when you wish.  But it is safe to modify the list by
hand when the minibuffer input functions are not using it.

@subsection Other Minibuffer Features

The @var{initial} argument to @code{read-from-minibufer} and other
minibuffer input functions can now be a cons cell @code{(@var{string}
. @var{position})}.  This means to start off with @var{string} in the
minibuffer, but put the cursor @var{position} characters from the
beginning, rather than at the end.

In @code{read-no-blanks-input}, the @var{initial} argument is now
optional; if it is omitted, the initial input string is the empty
string.

@section New Features for Defining Commands

@itemize @bullet
@item
If the interactive specification begins with @samp{@@}, this means to
select the window under the mouse.  This selection takes place before
doing anything else with the command.

You can use both @samp{@@} and @samp{*} together in one command; they
are processed in order of appearance.

@item
Prompts in an interactive specification can incorporate the values of
the preceding arguments.  Emacs replaces @samp{%}-sequences (as used
with the @code{format} function) in the prompt with the interactive
arguments that have been read so far.  For example, a command with this
interactive specification

@example
(interactive "sReplace: \nsReplace %s with: ")
@end example

@noindent
prompts for the first argument with @samp{Replace: }, and then prompts
for the second argument with @samp{Replace @var{foo} with: }, where
@var{foo} is the string read as the first argument.

@item
If a command name has a property @code{enable-recursive-minibuffers}
which is non-@code{nil}, then the command can use the minibuffer to read
arguments even if it is invoked from the minibuffer.  The minibuffer
command @code{next-matching-history-element} (normally bound to
@kbd{M-s} in the minibuffer) uses this feature.
@end itemize

@section New Features for Reading Input

@itemize @bullet
@item
The function @code{set-input-mode} now takes four arguments.  The last
argument is optional.  Their names are @var{interrupt}, @var{flow},
@var{meta} and @var{quit}.

The argument @var{interrupt} says whether to use interrupt-driven
input.  Non-@code{nil} means yes, and @code{nil} means no (use CBREAK
mode).

The argument @var{flow} says whether to enable terminal flow control.
Non-@code{nil} means yes.

The argument @var{meta} says whether to enable the use of a Meta key.
Non-@code{nil} means yes.

If @var{quit} non-@code{nil}, it is the character to use for quitting.
(Normally this is @kbd{C-g}.)

@item
The variable @code{meta-flag} has been deleted; use
@code{set-input-mode} to enable or disable support for a @key{META}
key.  This change was made because @code{set-input-mode} can send the
terminal the appropriate commands to enable or disable operation of the
@key{META} key.

@item
The new variable @code{extra-keyboard-modifiers} lets Lisp programs
``press'' the modifier keys on the keyboard.
The value is a bit mask:

@table @asis
@item 1
The @key{SHIFT} key.
@item 2
The @key{LOCK} key.
@item 4
The @key{CTL} key.
@item 8
The @key{META} key.
@end table

When you use X windows, the program can press any of the modifier keys
in this way.  Otherwise, only the @key{CTL} and @key{META} keys can be
virtually pressed.

@item
You can use the new function @code{keyboard-translate} to set up 
@code{keyboard-translate-table} conveniently.

@item
Y-or-n questions using the @code{y-or-n-p} function now accept @kbd{C-]}
(usually mapped to @code{abort-recursive-edit}) as well as @kbd{C-g} to
quit.

@item
The variable @code{num-input-keys} is the total number of key sequences 
that the user has typed during this Emacs session.

@item
A new Lisp variable, @code{function-key-map}, holds a keymap which
describes the character sequences sent by function keys on an ordinary
character terminal.  This uses the same keymap data structure that is
used to hold bindings of key sequences, but it has a different meaning:
it specifies translations to make while reading a key sequence.

If @code{function-key-map} ``binds'' a key sequence @var{k} to a vector
@var{v}, then when @var{k} appears as a subsequence @emph{anywhere} in a
key sequence, it is replaced with @var{v}.

For example, VT100 terminals send @kbd{@key{ESC} O P} when the ``keypad''
PF1 key is pressed.  Thus, on a VT100, @code{function-key-map} should
``bind'' that sequence to @code{[pf1]}.  This specifies translation of
@kbd{@key{ESC} O P} into @key{PF1} anywhere in a key sequence.

Thus, typing @kbd{C-c @key{PF1}} sends the character sequence @kbd{C-c
@key{ESC} O P}, but @code{read-key-sequence} translates this back into
@kbd{C-c @key{PF1}}, which it returns as the vector @code{[?\C-c PF1]}.

Entries in @code{function-key-map} are ignored if they conflict with
bindings made in the minor mode, local, or global keymaps.

The value of @code{function-key-map} is usually set up automatically
according to the terminal's Terminfo or Termcap entry, and the
terminal-specific Lisp files.  Emacs comes with a number of
terminal-specific files for many common terminals; their main purpose is
to make entries in @code{function-key-map} beyond those that can be
deduced from Termcap and Terminfo.

@item
The variable @code{key-translation-map} works like @code{function-key-map}
except for two things:

@itemize @bullet
@item
@code{key-translation-map} goes to work after @code{function-key-map} is
finished; it receives the results of translation by
@code{function-key-map}.

@item
@code{key-translation-map} overrides actual key bindings.
@end itemize

The intent of @code{key-translation-map} is for users to map one
character set to another, including ordinary characters normally bound
to @code{self-insert-command}.
@end itemize

@section New Syntax Table Features

@itemize @bullet
@item
You can use two new functions to move across characters in certain
syntax classes.

@code{skip-syntax-forward} moves point forward across characters whose
syntax classes are mentioned in its first argument, a string.  It stops
when it encounters the end of the buffer, or position @var{lim} (the
optional second argument), or a character it is not supposed to skip.
The function @code{skip-syntax-backward} is similar but moves backward.

@item
The new function @code{forward-comment} moves point by comments.  It
takes one argument, @var{count}; it moves point forward across
@var{count} comments (backward, if @var{count} is negative).  If it
finds anything other than a comment or whitespace, it stops, leaving
point at the far side of the last comment found.  It also stops after
satisfying @var{count}.

@item
The new variable @code{words-include-escapes} affects the behavior of
@code{forward-word} and everything that uses it.  If it is
non-@code{nil}, then characters in the ``escape'' and ``character
quote'' syntax classes count as part of words.

@item
There are two new syntax flags for use in syntax tables.

@itemize -
@item
The prefix flag.

The @samp{p} flag identifies additional ``prefix characters'' in Lisp
syntax.  You can set this flag with @code{modify-syntax-entry} by
including the letter @samp{p} in the syntax specification.

These characters are treated as whitespace when they appear between
expressions.  When they appear withing an expression, they are handled
according to their usual syntax codes.

The function @code{backward-prefix-chars} moves back over these
characters, as well as over characters whose primary syntax class is
prefix (@samp{'}).

@item
The @samp{b} comment style flag.

Emacs can now supports two comment styles simultaneously.  (This is for
the sake of C++.)  More specifically, it can recognize two different
comment-start sequences.  Both must share the same first character; only
the second character may differ.  Mark the second character of the
@samp{b}-style comment start sequence with the @samp{b} flag.  You can
set this flag with @code{modify-syntax-entry} by including the letter
@samp{b} in the syntax specification.

The two styles of comment can have different comment-end sequences.  A
comment-end sequence (one or two characters) applies to the @samp{b}
style if its first character has the @samp{b} flag set; otherwise, it
applies to the @samp{a} style.

The appropriate comment syntax settings for C++ are as follows:

@table @asis
@item @samp{/}
@samp{124b}
@item @samp{*}
@samp{23}
@item newline
@samp{>b}
@end table

Thus @samp{/*} is a comment-start sequence for @samp{a} style, @samp{//}
is a comment-start sequence for @samp{b} style, @samp{*/} is a
comment-end sequence for @samp{a} style, and newline is a comment-end
sequence for @samp{b} style.
@end itemize
@end itemize

@section The Case Table

You can customize case conversion using the new case table feature.  A
case table is a collection of strings that specifies the mapping between
upper case and lower case letters.  Each buffer has its own case table.
You need a case table if you are using a language which has letters that
are not standard ASCII letters.

A case table is a list of this form:

@example
(@var{downcase} @var{upcase} @var{canonicalize} @var{equivalences})
@end example

@noindent
where each element is either @code{nil} or a string of length 256.  The
element @var{downcase} says how to map each character to its lower-case
equivalent.  The element @var{upcase} maps each character to its
upper-case equivalent.  If lower and upper case characters are in 1-1
correspondence, use @code{nil} for @var{upcase}; then Emacs deduces the
upcase table from @var{downcase}.

For some languages, upper and lower case letters are not in 1-1
correspondence.  There may be two different lower case letters with the
same upper case equivalent.  In these cases, you need to specify the
maps for both directions.

The element @var{canonicalize} maps each character to a canonical
equivalent; any two characters that are related by case-conversion have
the same canonical equivalent character.

The element @var{equivalences} is a map that cyclicly permutes each
equivalence class (of characters with the same canonical equivalent).

You can provide @code{nil} for both @var{canonicalize} and
@var{equivalences}, in which case both are deduced from @var{downcase}
and @var{upcase}.

Here are the functions for working with case tables:

@code{case-table-p} is a predicate that says whether a Lisp object is a
valid case table.

@code{set-standard-case-table} takes one argument and makes that
argument the case table for new buffers created subsequently.
@code{standard-case-table} returns the current value of the new buffer
case table.

@code{current-case-table} returns the case table of the current buffer.
@code{set-case-table} sets the current buffer's case table to the
argument.

@code{set-case-syntax-pair} is a convenient function for specifying a
pair of letters, upper case and lower case.  Call it with two arguments,
the upper case letter and the lower case letter.  It modifies the
standard case table and a few syntax tables that are predefined in
Emacs.  This function is intended as a subroutine for packages that
define non-ASCII character sets.

Load the library @file{iso-syntax} to set up the syntax and case table for
the 256 bit ISO Latin 1 character set.

@section New Features for Dealing with Buffers

@itemize @bullet
@item
The new function @code{buffer-modified-tick} returns a buffer's
modification-count that ticks every time the buffer is modified.  It
takes one optional argument, which is the buffer you want to examine.
If the argument is @code{nil} (or omitted), the current buffer is used.

@item
@code{buffer-disable-undo} is a new name for the function
formerly known as @code{buffer-flush-undo}.  This turns off recording
of undo information in the buffer given as argument.

@item
The new function @code{generate-new-buffer-name} chooses a name that
would be unique for a new buffer---but does not create the buffer.  Give
it one argument, a starting name.  It produces a name not in use for a
buffer by appending a number inside of @samp{<@dots{}>}.

@item
The function @code{rename-buffer} now takes an option second argument
which tells it that if the specified new name corresponds to an existing
buffer, it should use @code{generate-new-buffer-name} to modify the name
to be unique, rather than signaling an error.

@code{rename-buffer} now returns the name to which the buffer was
renamed.

@item
The function @code{list-buffers} now looks at the local variable
@code{list-buffers-directory} in each non-file-visiting buffer, and
shows its value where the file would normally go.  Dired sets this
variable in each Dired buffer, so the buffer list now shows which
directory each Dired buffer is editing.

@item
The function @code{other-buffer} now takes an optional second argument
@var{visible-ok} which, if non-@code{nil}, indicates that buffers
currently being displayed in windows may be returned even if there are
other buffers not visible.  Normally, @code{other-buffer} returns a
currently visible buffer only as a last resort, if there are no suitable
nonvisible buffers.

@item
The hook @code{kill-buffer-hook} now runs whenever a buffer is killed.
@end itemize

@section Local Variables Features

@itemize @bullet
@item
If a local variable name has a non-@code{nil} @code{permanent-local}
property, then @code{kill-all-local-variables} does not kill it.  Such
local variables are ``permanent''---they remain unchanged even if you
select a different major mode.

Permanent locals are useful when they have to do with where the file
came from or how to save it, rather than with how to edit the contents.

@item
The function @code{make-local-variable} now never changes the value of the variable
that it makes local.  If the variable had no value before, it still has
no value after becoming local.

@item
The new function @code{default-boundp} tells you whether a variable has
a default value (as opposed to being unbound in its default value).  If
@code{(default-boundp 'foo)} returns @code{nil}, then
@code{(default-value 'foo)} would get an error.

@code{default-boundp} is to @code{default-value} as @code{boundp} is to
@code{symbol-value}.

@item
The special forms @code{defconst} and @code{defvar}, when the variable
is local in the current buffer, now set the variable's default value
rather than its local value.
@end itemize

@section New Features for Subprocesses

@itemize @bullet
@item
@code{call-process} and @code{call-process-region} now return a value
that indicates how the synchronous subprocess terminated.  It is either
a number, which is the exit status of a process, or a signal name
represented as a string.

@item
@code{process-status} now returns @code{open} and @code{closed} as the
status values for network connections.

@item
The standard asynchronous subprocess features work on VMS now,
and the special VMS asynchronous subprocess functions have been deleted.

@item
You can use the transaction queue feature for more convenient
communication with subprocesses using transactions.

Call @code{tq-create} to create a transaction queue communicating with a
specified process.  Then you can call @code{tq-enqueue} to send a
transaction.  @code{tq-enqueue} takes these five arguments:

@example
(tq-enqueue @var{tq} @var{question} @var{regexp} @var{closure} @var{fn})
@end example

@var{tq} is the queue to use.  (Specifying the queue has the effect of
specifying the process to talk to.)  The argument @var{question} is the
outgoing message which starts the transaction.  The argument @var{fn} is
the function to call when the corresponding answer comes back; it is
called with two arguments: @var{closure}, and the answer received.

The argument @var{regexp} is a regular expression to match the entire
answer; that's how @code{tq-enqueue} tells where the answer ends.

Call @code{tq-close} to shut down a transaction queue and terminate its
subprocess.

@item 
The function @code{signal-process} sends a signal to process @var{pid},
which need not be a child of Emacs.  The second argument @var{signal}
specifies which signal to send; it should be an integer.
@end itemize

@section New Features for Dealing with Times And Time Delays

@itemize @bullet
@item
The new function @code{current-time} returns the system's time value as
a list of three integers: @code{(@var{high} @var{low} @var{microsec})}.
The integers @var{high} and @var{low} combine to give the number of
seconds since 0:00 January 1, 1970, which is @var{high} * 2**16 +
@var{low}.

@var{microsec} gives the microseconds since the start of the current
second (or 0 for systems that return time only on the resolution of a
second).

@item
The function @code{current-time-string} accepts an optional argument
@var{time-value}.  If given, this specifies a time to format instead of
the current time.  The argument should be a cons cell containing two
integers, or a list whose first two elements are integers.  Thus, you
can use times obtained from @code{current-time} (see above) and from
@code{file-attributes}.

@item
You can now find out the user's time zone using @code{current-time-zone}.
It takes no arguments, and returns a list of this form:

@example
(@var{offset} @var{savings-flag} @var{standard} @var{savings})
@end example

@var{offset} is an integer specifying how many minutes east of Greenwich
the current time zone is located.  A negative value means west of
Greenwich.  Note that this describes the standard time; if daylight
savings time is in effect, it does not affect this value.

@var{savings-flag} is non-@code{nil} iff daylight savings time or some other
sort of seasonal time adjustment is in effect.

@var{standard} is a string giving the name of the time zone when no
seasonal time adjustment is in effect.

@var{savings} is a string giving the name of the time zone when there is a
seasonal time adjustment in effect.

If the user has specified a region that does not use a seasonal time
adjustment, @var{savings-flag} is always @code{nil}, and @var{standard}
and @var{savings} are equal.

@item
@code{sit-for}, @code{sleep-for} now let you specify the time period in
milliseconds as well as in seconds.  The first argument gives the number
of seconds, as before, and the optional second argument gives additional
milliseconds.  The time periods specified by these two arguments are
added together.

Not all systems support this; you get an error if you specify nonzero
milliseconds and it isn't supported.

@code{sit-for} also accepts an optional third argument @var{nodisp}.  If
this is non-@code{nil}, @code{sit-for} does not redisplay.  It still
waits for the specified time or until input is available.

@item
@code{accept-process-output} now accepts a timeout specified by optional
second and third arguments.  The second argument specifies the number of
seconds, while the third specifies the number of milliseconds.  The time
periods specified by these two arguments are added together.

Not all systems support this; you get an error if you specify nonzero
milliseconds and it isn't supported.

The function returns @code{nil} if the timeout expired before output
arrived, or non-@code{nil} if it did get some output.

@item
You can set up a timer to call a function at a specified future time.
To do so, call @code{run-at-time}, like this:

@example
(run-at-time @var{time} @var{repeat} @var{function} @var{args}@dots{})
@end example

Here, @var{time} is a string saying when to call the function.  The
argument @var{function} is the function to call later, and @var{args}
are the arguments to give it when it is called.

The argument @var{repeat} specifies how often to repeat the call.  If
@var{repeat} is @code{nil}, there are no repetitions; @var{function} is
called just once, at @var{time}.  If @var{repeat} is an integer, it
specifies a repetition period measured in seconds.

Absolute times may be specified in a wide variety of formats; The form
@samp{@var{hour}:@var{min}:@var{sec} @var{timezone}
@var{month}/@var{day}/@var{year}}, where all fields are numbers, works;
the format that @code{current-time-string} returns is also allowed.

To specify a relative time, use numbers followed by units.
For example:

@table @samp
@item 1 min
denotes 1 minute from now.
@item 1 min 5 sec
denotes 65 seconds from now.
@item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
denotes exactly 103 months, 123 days, and 10862 seconds from now.
@end table

If @var{time} is an integer, that specifies a relative time measured in
seconds.
@end itemize

To cancel the requested future action, pass the value that @code{run-at-time}
returned to the function @code{cancel-timer}.

@section Profiling Lisp Programs

You can now make execution-time profiles of Emacs Lisp programs using
the @file{profile} library.  See the file @file{profile.el} for
instructions; if you have written a Lisp program big enough to be worth
profiling, you can surely understand them.

@section New Features for Lisp Debuggers

@itemize @bullet
@item
You can now specify which kinds of errors should invoke the Lisp
debugger by setting the variable @code{debug-on-error} to a list of error
conditions.  For example, if you set it to the list @code{(void-variable)},
then only errors about a variable that has no value invoke the
debugger.

@item
The variable @code{command-debug-status} is used by Lisp debuggers.  It
records the debugging status of current interactive command.  Each time
a command is called interactively, this variable is bound to
@code{nil}.  The debugger can set this variable to leave information for
future debugger invocations during the same command.

The advantage of this variable over some other variable in the debugger
itself is that the data will not be visible for any other command
invocation.

@item
The function @code{backtrace-frame} is intended for use in Lisp
debuggers.  It returns information about what a frame on the Lisp call
stack is doing.  You specify one argument, which is the number of stack
frames to count up from the current execution point.

If that stack frame has not evaluated the arguments yet (or is a special
form), the value is @code{(nil @var{function} @var{arg-forms}@dots{})}.

If that stack frame has evaluated its arguments and called its function
already, the value is @code{(t @var{function}
@var{arg-values}@dots{})}.

In the return value, @var{function} is whatever was supplied as @sc{car}
of evaluated list, or a @code{lambda} expression in the case of a macro
call.  If the function has a @code{&rest} argument, that is represented
as the tail of the list @var{arg-values}.

If the argument is out of range, @code{backtrace-frame} returns
@code{nil}.
@end itemize

@ignore

@item
@code{kill-ring-save} now gives visual feedback to indicate the region
of text being added to the kill ring.  If the opposite end of the
region is visible in the current window, the cursor blinks there.
Otherwise, some text from the other end of the region is displayed in
the message area.
@end ignore

@section Memory Allocation Changes

The list that @code{garbage-collect} returns now has one additional
element.  This is a cons cell containing two numbers.  It gives
information about the number of used and free floating point numbers,
much as the first element gives such information about the number of
used and free cons cells.

The new function @code{memory-limit} returns an indication of the last
address allocated by Emacs.  More precisely, it returns that address
divided by 1024.  You can use this to get a general idea of how your
actions affect the memory usage.

@section Hook Changes

@itemize @bullet
@item
Expanding an abbrev first runs the new hook
@code{pre-abbrev-expand-hook}.

@item
The editor command loop runs the normal hook @code{pre-command-hook}
before each command, and runs @code{post-command-hook} after each
command.

@item
Auto-saving runs the new hook @code{auto-save-hook} before actually
starting to save any files.

@item
The new variable @code{revert-buffer-insert-file-contents-function}
holds a function that @code{revert-buffer} now uses to read in the
contents of the reverted buffer---instead of calling
@code{insert-file-contents}.

@item
The variable @code{lisp-indent-hook} has been renamed to
@code{lisp-indent-function}.

@item
The variable @code{auto-fill-hook} has been renamed to
@code{auto-fill-function}.

@item
The variable @code{blink-paren-hook} has been renamed to
@code{blink-paren-function}.

@item
The variable @code{temp-buffer-show-hook} has been renamed to
@code{temp-buffer-show-function}.

@item
The variable @code{suspend-hook} has been renamed to
@code{suspend-hooks}, because it is a list of functions but is not a
normal hook.

@item
The new function @code{add-hook} provides a handy way to add a function
to a hook variable.  For example,

@example
(add-hook 'text-mode-hook 'my-text-hook-function)
@end example

@noindent
arranges to call @code{my-text-hook-function}
when entering Text mode or related modes.
@end itemize

@bye
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.