Source

emacs / lispref / positions.texi

Full commit
   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
@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000, 2001,
@c   2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/positions
@node Positions, Markers, Frames, Top
@chapter Positions
@cindex position (in buffer)

  A @dfn{position} is the index of a character in the text of a buffer.
More precisely, a position identifies the place between two characters
(or before the first character, or after the last character), so we can
speak of the character before or after a given position.  However, we
often speak of the character ``at'' a position, meaning the character
after that position.

  Positions are usually represented as integers starting from 1, but
can also be represented as @dfn{markers}---special objects that
relocate automatically when text is inserted or deleted so they stay
with the surrounding characters.  Functions that expect an argument to
be a position (an integer), but accept a marker as a substitute,
normally ignore which buffer the marker points into; they convert the
marker to an integer, and use that integer, exactly as if you had
passed the integer as the argument, even if the marker points to the
``wrong'' buffer.  A marker that points nowhere cannot convert to an
integer; using it instead of an integer causes an error.
@xref{Markers}.

  See also the ``field'' feature (@pxref{Fields}), which provides
functions that are used by many cursor-motion commands.

@menu
* Point::         The special position where editing takes place.
* Motion::        Changing point.
* Excursions::    Temporary motion and buffer changes.
* Narrowing::     Restricting editing to a portion of the buffer.
@end menu

@node Point
@section Point
@cindex point

  @dfn{Point} is a special buffer position used by many editing
commands, including the self-inserting typed characters and text
insertion functions.  Other commands move point through the text
to allow editing and insertion at different places.

  Like other positions, point designates a place between two characters
(or before the first character, or after the last character), rather
than a particular character.  Usually terminals display the cursor over
the character that immediately follows point; point is actually before
the character on which the cursor sits.

@cindex point with narrowing
  The value of point is a number no less than 1, and no greater than the
buffer size plus 1.  If narrowing is in effect (@pxref{Narrowing}), then
point is constrained to fall within the accessible portion of the buffer
(possibly at one end of it).

  Each buffer has its own value of point, which is independent of the
value of point in other buffers.  Each window also has a value of point,
which is independent of the value of point in other windows on the same
buffer.  This is why point can have different values in various windows
that display the same buffer.  When a buffer appears in only one window,
the buffer's point and the window's point normally have the same value,
so the distinction is rarely important.  @xref{Window Point}, for more
details.

@defun point
@cindex current buffer position
This function returns the value of point in the current buffer,
as an integer.

@need 700
@example
@group
(point)
     @result{} 175
@end group
@end example
@end defun

@defun point-min
This function returns the minimum accessible value of point in the
current buffer.  This is normally 1, but if narrowing is in effect, it
is the position of the start of the region that you narrowed to.
(@xref{Narrowing}.)
@end defun

@defun point-max
This function returns the maximum accessible value of point in the
current buffer.  This is @code{(1+ (buffer-size))}, unless narrowing is
in effect, in which case it is the position of the end of the region
that you narrowed to.  (@xref{Narrowing}.)
@end defun

@defun buffer-end flag
This function returns @code{(point-max)} if @var{flag} is greater than
0, @code{(point-min)} otherwise.  The argument @var{flag} must be a
number.
@end defun

@defun buffer-size &optional buffer
This function returns the total number of characters in the current
buffer.  In the absence of any narrowing (@pxref{Narrowing}),
@code{point-max} returns a value one larger than this.

If you specify a buffer, @var{buffer}, then the value is the
size of @var{buffer}.

@example
@group
(buffer-size)
     @result{} 35
@end group
@group
(point-max)
     @result{} 36
@end group
@end example
@end defun

@node Motion
@section Motion
@cindex motion by chars, words, lines, lists

  Motion functions change the value of point, either relative to the
current value of point, relative to the beginning or end of the buffer,
or relative to the edges of the selected window.  @xref{Point}.

@menu
* Character Motion::       Moving in terms of characters.
* Word Motion::            Moving in terms of words.
* Buffer End Motion::      Moving to the beginning or end of the buffer.
* Text Lines::             Moving in terms of lines of text.
* Screen Lines::           Moving in terms of lines as displayed.
* List Motion::            Moving by parsing lists and sexps.
* Skipping Characters::    Skipping characters belonging to a certain set.
@end menu

@node Character Motion
@subsection Motion by Characters

  These functions move point based on a count of characters.
@code{goto-char} is the fundamental primitive; the other functions use
that.

@deffn Command goto-char position
This function sets point in the current buffer to the value
@var{position}.  If @var{position} is less than 1, it moves point to the
beginning of the buffer.  If @var{position} is greater than the length
of the buffer, it moves point to the end.

If narrowing is in effect, @var{position} still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion.  If @var{position} is out of range, @code{goto-char} moves
point to the beginning or the end of the accessible portion.

When this function is called interactively, @var{position} is the
numeric prefix argument, if provided; otherwise it is read from the
minibuffer.

@code{goto-char} returns @var{position}.
@end deffn

@deffn Command forward-char &optional count
@c @kindex beginning-of-buffer
@c @kindex end-of-buffer
This function moves point @var{count} characters forward, towards the
end of the buffer (or backward, towards the beginning of the buffer, if
@var{count} is negative).  If @var{count} is @code{nil}, the default
is 1.

If this attempts to move past the beginning or end of the buffer (or
the limits of the accessible portion, when narrowing is in effect), it
signals an error with error symbol @code{beginning-of-buffer} or
@code{end-of-buffer}.

In an interactive call, @var{count} is the numeric prefix argument.
@end deffn

@deffn Command backward-char &optional count
This is just like @code{forward-char} except that it moves
in the opposite direction.
@end deffn

@node Word Motion
@subsection Motion by Words

  These functions for parsing words use the syntax table to decide
whether a given character is part of a word.  @xref{Syntax Tables}.

@deffn Command forward-word &optional count
This function moves point forward @var{count} words (or backward if
@var{count} is negative).  If @var{count} is @code{nil}, it moves
forward one word.

``Moving one word'' means moving until point crosses a
word-constituent character and then encounters a word-separator
character.  However, this function cannot move point past the boundary
of the accessible portion of the buffer, or across a field boundary
(@pxref{Fields}).  The most common case of a field boundary is the end
of the prompt in the minibuffer.

If it is possible to move @var{count} words, without being stopped
prematurely by the buffer boundary or a field boundary, the value is
@code{t}.  Otherwise, the return value is @code{nil} and point stops at
the buffer boundary or field boundary.

If @code{inhibit-field-text-motion} is non-@code{nil},
this function ignores field boundaries.

In an interactive call, @var{count} is specified by the numeric prefix
argument.  If @var{count} is omitted or @code{nil}, it defaults to 1.
@end deffn

@deffn Command backward-word &optional count
This function is just like @code{forward-word}, except that it moves
backward until encountering the front of a word, rather than forward.
@end deffn

@defvar words-include-escapes
@c Emacs 19 feature
This variable 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.  Otherwise, they do not.
@end defvar

@defvar inhibit-field-text-motion
If this variable is non-@code{nil}, certain motion functions including
@code{forward-word}, @code{forward-sentence}, and
@code{forward-paragraph} ignore field boundaries.
@end defvar

@node Buffer End Motion
@subsection Motion to an End of the Buffer
@cindex move to beginning or end of buffer

  To move point to the beginning of the buffer, write:

@example
@group
(goto-char (point-min))
@end group
@end example

@noindent
Likewise, to move to the end of the buffer, use:

@example
@group
(goto-char (point-max))
@end group
@end example

  Here are two commands that users use to do these things.  They are
documented here to warn you not to use them in Lisp programs, because
they set the mark and display messages in the echo area.

@deffn Command beginning-of-buffer &optional n
This function moves point to the beginning of the buffer (or the limits
of the accessible portion, when narrowing is in effect), setting the
mark at the previous position (except in Transient Mark mode, if
the mark is already active, it does not set the mark.)

If @var{n} is non-@code{nil}, then it puts point @var{n} tenths of the
way from the beginning of the accessible portion of the buffer.  In an
interactive call, @var{n} is the numeric prefix argument, if provided;
otherwise @var{n} defaults to @code{nil}.

@strong{Warning:} Don't use this function in Lisp programs!
@end deffn

@deffn Command end-of-buffer &optional n
This function moves point to the end of the buffer (or the limits of
the accessible portion, when narrowing is in effect), setting the mark
at the previous position (except in Transient Mark mode when the mark
is already active).  If @var{n} is non-@code{nil}, then it puts point
@var{n} tenths of the way from the end of the accessible portion of
the buffer.

In an interactive call, @var{n} is the numeric prefix argument,
if provided; otherwise @var{n} defaults to @code{nil}.

@strong{Warning:} Don't use this function in Lisp programs!
@end deffn

@node Text Lines
@subsection Motion by Text Lines
@cindex lines

  Text lines are portions of the buffer delimited by newline characters,
which are regarded as part of the previous line.  The first text line
begins at the beginning of the buffer, and the last text line ends at
the end of the buffer whether or not the last character is a newline.
The division of the buffer into text lines is not affected by the width
of the window, by line continuation in display, or by how tabs and
control characters are displayed.

@deffn Command goto-line line
This function moves point to the front of the @var{line}th line,
counting from line 1 at beginning of the buffer.  If @var{line} is less
than 1, it moves point to the beginning of the buffer.  If @var{line} is
greater than the number of lines in the buffer, it moves point to the
end of the buffer---that is, the @emph{end of the last line} of the
buffer.  This is the only case in which @code{goto-line} does not
necessarily move to the beginning of a line.

If narrowing is in effect, then @var{line} still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion.  So @code{goto-line} moves point to the beginning or end of the
accessible portion, if the line number specifies an inaccessible
position.

The return value of @code{goto-line} is the difference between
@var{line} and the line number of the line to which point actually was
able to move (in the full buffer, before taking account of narrowing).
Thus, the value is positive if the scan encounters the real end of the
buffer before finding the specified line.  The value is zero if scan
encounters the end of the accessible portion but not the real end of the
buffer.

In an interactive call, @var{line} is the numeric prefix argument if
one has been provided.  Otherwise @var{line} is read in the minibuffer.
@end deffn

@deffn Command beginning-of-line &optional count
This function moves point to the beginning of the current line.  With an
argument @var{count} not @code{nil} or 1, it moves forward
@var{count}@minus{}1 lines and then to the beginning of the line.

This function does not move point across a field boundary
(@pxref{Fields}) unless doing so would move beyond there to a
different line; therefore, if @var{count} is @code{nil} or 1, and
point starts at a field boundary, point does not move.  To ignore
field boundaries, either bind @code{inhibit-field-text-motion} to
@code{t}, or use the @code{forward-line} function instead.  For
instance, @code{(forward-line 0)} does the same thing as
@code{(beginning-of-line)}, except that it ignores field boundaries.

If this function reaches the end of the buffer (or of the accessible
portion, if narrowing is in effect), it positions point there.  No error
is signaled.
@end deffn

@defun line-beginning-position &optional count
Return the position that @code{(beginning-of-line @var{count})}
would move to.
@end defun

@deffn Command end-of-line &optional count
This function moves point to the end of the current line.  With an
argument @var{count} not @code{nil} or 1, it moves forward
@var{count}@minus{}1 lines and then to the end of the line.

This function does not move point across a field boundary
(@pxref{Fields}) unless doing so would move beyond there to a
different line; therefore, if @var{count} is @code{nil} or 1, and
point starts at a field boundary, point does not move.  To ignore
field boundaries, bind @code{inhibit-field-text-motion} to @code{t}.

If this function reaches the end of the buffer (or of the accessible
portion, if narrowing is in effect), it positions point there.  No error
is signaled.
@end deffn

@defun line-end-position &optional count
Return the position that @code{(end-of-line @var{count})}
would move to.
@end defun

@deffn Command forward-line &optional count
@cindex beginning of line
This function moves point forward @var{count} lines, to the beginning of
the line.  If @var{count} is negative, it moves point
@minus{}@var{count} lines backward, to the beginning of a line.  If
@var{count} is zero, it moves point to the beginning of the current
line.  If @var{count} is @code{nil}, that means 1.

If @code{forward-line} encounters the beginning or end of the buffer (or
of the accessible portion) before finding that many lines, it sets point
there.  No error is signaled.

@code{forward-line} returns the difference between @var{count} and the
number of lines actually moved.  If you attempt to move down five lines
from the beginning of a buffer that has only three lines, point stops at
the end of the last line, and the value will be 2.

In an interactive call, @var{count} is the numeric prefix argument.
@end deffn

@defun count-lines start end
@cindex lines in region
@anchor{Definition of count-lines}
This function returns the number of lines between the positions
@var{start} and @var{end} in the current buffer.  If @var{start} and
@var{end} are equal, then it returns 0.  Otherwise it returns at least
1, even if @var{start} and @var{end} are on the same line.  This is
because the text between them, considered in isolation, must contain at
least one line unless it is empty.

Here is an example of using @code{count-lines}:

@example
@group
(defun current-line ()
  "Return the vertical position of point@dots{}"
  (+ (count-lines (window-start) (point))
     (if (= (current-column) 0) 1 0)))
@end group
@end example
@end defun

@defun line-number-at-pos &optional pos
@cindex line number
This function returns the line number in the current buffer
corresponding to the buffer position @var{pos}.  If @var{pos} is @code{nil}
or omitted, the current buffer position is used.
@end defun

@ignore
@c ================
The @code{previous-line} and @code{next-line} commands are functions
that should not be used in programs.  They are for users and are
mentioned here only for completeness.

@deffn Command previous-line count
@cindex goal column
This function moves point up @var{count} lines (down if @var{count}
is negative).  In moving, it attempts to keep point in the ``goal column''
(normally the same column that it was at the beginning of the move).

If there is no character in the target line exactly under the current
column, point is positioned after the character in that line which
spans this column, or at the end of the line if it is not long enough.

If it attempts to move beyond the top or bottom of the buffer (or clipped
region), then point is positioned in the goal column in the top or
bottom line.  No error is signaled.

In an interactive call, @var{count} will be the numeric
prefix argument.

The command @code{set-goal-column} can be used to create a semipermanent
goal column to which this command always moves.  Then it does not try to
move vertically.

If you are thinking of using this in a Lisp program, consider using
@code{forward-line} with a negative argument instead.  It is usually easier
to use and more reliable (no dependence on goal column, etc.).
@end deffn

@deffn Command next-line count
This function moves point down @var{count} lines (up if @var{count}
is negative).  In moving, it attempts to keep point in the ``goal column''
(normally the same column that it was at the beginning of the move).

If there is no character in the target line exactly under the current
column, point is positioned after the character in that line which
spans this column, or at the end of the line if it is not long enough.

If it attempts to move beyond the top or bottom of the buffer (or clipped
region), then point is positioned in the goal column in the top or
bottom line.  No error is signaled.

In the case where the @var{count} is 1, and point is on the last
line of the buffer (or clipped region), a new empty line is inserted at the
end of the buffer (or clipped region) and point moved there.

In an interactive call, @var{count} will be the numeric
prefix argument.

The command @code{set-goal-column} can be used to create a semipermanent
goal column to which this command always moves.  Then it does not try to
move vertically.

If you are thinking of using this in a Lisp program, consider using
@code{forward-line} instead.  It is usually easier
to use and more reliable (no dependence on goal column, etc.).
@end deffn

@c ================
@end ignore

  Also see the functions @code{bolp} and @code{eolp} in @ref{Near Point}.
These functions do not move point, but test whether it is already at the
beginning or end of a line.

@node Screen Lines
@subsection Motion by Screen Lines

  The line functions in the previous section count text lines, delimited
only by newline characters.  By contrast, these functions count screen
lines, which are defined by the way the text appears on the screen.  A
text line is a single screen line if it is short enough to fit the width
of the selected window, but otherwise it may occupy several screen
lines.

  In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines.  In these cases,
@code{vertical-motion} moves point much like @code{forward-line}.
@xref{Truncation}.

  Because the width of a given string depends on the flags that control
the appearance of certain characters, @code{vertical-motion} behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows).  @xref{Usual
Display}.

  These functions scan text to determine where screen lines break, and
thus take time proportional to the distance scanned.  If you intend to
use them heavily, Emacs provides caches which may improve the
performance of your code.  @xref{Truncation, cache-long-line-scans}.

@defun vertical-motion count &optional window
This function moves point to the start of the screen line @var{count}
screen lines down from the screen line containing point.  If @var{count}
is negative, it moves up instead.

@code{vertical-motion} returns the number of screen lines over which it
moved point.  The value may be less in absolute value than @var{count}
if the beginning or end of the buffer was reached.

The window @var{window} is used for obtaining parameters such as the
width, the horizontal scrolling, and the display table.  But
@code{vertical-motion} always operates on the current buffer, even if
@var{window} currently displays some other buffer.
@end defun

@defun count-screen-lines &optional beg end count-final-newline window
This function returns the number of screen lines in the text from
@var{beg} to @var{end}.  The number of screen lines may be different
from the number of actual lines, due to line continuation, the display
table, etc.  If @var{beg} and @var{end} are @code{nil} or omitted,
they default to the beginning and end of the accessible portion of the
buffer.

If the region ends with a newline, that is ignored unless the optional
third argument @var{count-final-newline} is non-@code{nil}.

The optional fourth argument @var{window} specifies the window for
obtaining parameters such as width, horizontal scrolling, and so on.
The default is to use the selected window's parameters.

Like @code{vertical-motion}, @code{count-screen-lines} always uses the
current buffer, regardless of which buffer is displayed in
@var{window}.  This makes possible to use @code{count-screen-lines} in
any buffer, whether or not it is currently displayed in some window.
@end defun

@deffn Command move-to-window-line count
This function moves point with respect to the text currently displayed
in the selected window.  It moves point to the beginning of the screen
line @var{count} screen lines from the top of the window.  If
@var{count} is negative, that specifies a position
@w{@minus{}@var{count}} lines from the bottom (or the last line of the
buffer, if the buffer ends above the specified screen position).

If @var{count} is @code{nil}, then point moves to the beginning of the
line in the middle of the window.  If the absolute value of @var{count}
is greater than the size of the window, then point moves to the place
that would appear on that screen line if the window were tall enough.
This will probably cause the next redisplay to scroll to bring that
location onto the screen.

In an interactive call, @var{count} is the numeric prefix argument.

The value returned is the window line number point has moved to, with
the top line in the window numbered 0.
@end deffn

@defun compute-motion from frompos to topos width offsets window
This function scans the current buffer, calculating screen positions.
It scans the buffer forward from position @var{from}, assuming that is
at screen coordinates @var{frompos}, to position @var{to} or coordinates
@var{topos}, whichever comes first.  It returns the ending buffer
position and screen coordinates.

The coordinate arguments @var{frompos} and @var{topos} are cons cells of
the form @code{(@var{hpos} . @var{vpos})}.

The argument @var{width} is the number of columns available to display
text; this affects handling of continuation lines.  @code{nil} means
the actual number of usable text columns in the window, which is
equivalent to the value returned by @code{(window-width window)}.

The argument @var{offsets} is either @code{nil} or a cons cell of the
form @code{(@var{hscroll} . @var{tab-offset})}.  Here @var{hscroll} is
the number of columns not being displayed at the left margin; most
callers get this by calling @code{window-hscroll}.  Meanwhile,
@var{tab-offset} is the offset between column numbers on the screen and
column numbers in the buffer.  This can be nonzero in a continuation
line, when the previous screen lines' widths do not add up to a multiple
of @code{tab-width}.  It is always zero in a non-continuation line.

The window @var{window} serves only to specify which display table to
use.  @code{compute-motion} always operates on the current buffer,
regardless of what buffer is displayed in @var{window}.

The return value is a list of five elements:

@example
(@var{pos} @var{hpos} @var{vpos} @var{prevhpos} @var{contin})
@end example

@noindent
Here @var{pos} is the buffer position where the scan stopped, @var{vpos}
is the vertical screen position, and @var{hpos} is the horizontal screen
position.

The result @var{prevhpos} is the horizontal position one character back
from @var{pos}.  The result @var{contin} is @code{t} if the last line
was continued after (or within) the previous character.

For example, to find the buffer position of column @var{col} of screen line
@var{line} of a certain window, pass the window's display start location
as @var{from} and the window's upper-left coordinates as @var{frompos}.
Pass the buffer's @code{(point-max)} as @var{to}, to limit the scan to
the end of the accessible portion of the buffer, and pass @var{line} and
@var{col} as @var{topos}.  Here's a function that does this:

@example
(defun coordinates-of-position (col line)
  (car (compute-motion (window-start)
                       '(0 . 0)
                       (point-max)
                       (cons col line)
                       (window-width)
                       (cons (window-hscroll) 0)
                       (selected-window))))
@end example

When you use @code{compute-motion} for the minibuffer, you need to use
@code{minibuffer-prompt-width} to get the horizontal position of the
beginning of the first screen line.  @xref{Minibuffer Contents}.
@end defun

@node List Motion
@comment  node-name,  next,  previous,  up
@subsection Moving over Balanced Expressions
@cindex sexp motion
@cindex Lisp expression motion
@cindex list motion
@cindex balanced parenthesis motion

  Here are several functions concerned with balanced-parenthesis
expressions (also called @dfn{sexps} in connection with moving across
them in Emacs).  The syntax table controls how these functions interpret
various characters; see @ref{Syntax Tables}.  @xref{Parsing
Expressions}, for lower-level primitives for scanning sexps or parts of
sexps.  For user-level commands, see @ref{Parentheses,, Commands for
Editing with Parentheses, emacs, The GNU Emacs Manual}.

@deffn Command forward-list &optional arg
This function moves forward across @var{arg} (default 1) balanced groups of
parentheses.  (Other syntactic entities such as words or paired string
quotes are ignored.)
@end deffn

@deffn Command backward-list &optional arg
This function moves backward across @var{arg} (default 1) balanced groups of
parentheses.  (Other syntactic entities such as words or paired string
quotes are ignored.)
@end deffn

@deffn Command up-list &optional arg
This function moves forward out of @var{arg} (default 1) levels of parentheses.
A negative argument means move backward but still to a less deep spot.
@end deffn

@deffn Command down-list &optional arg
This function moves forward into @var{arg} (default 1) levels of
parentheses.  A negative argument means move backward but still go
deeper in parentheses (@minus{}@var{arg} levels).
@end deffn

@deffn Command forward-sexp &optional arg
This function moves forward across @var{arg} (default 1) balanced expressions.
Balanced expressions include both those delimited by parentheses and
other kinds, such as words and string constants.
@xref{Parsing Expressions}.  For example,

@example
@group
---------- Buffer: foo ----------
(concat@point{} "foo " (car x) y z)
---------- Buffer: foo ----------
@end group

@group
(forward-sexp 3)
     @result{} nil

---------- Buffer: foo ----------
(concat "foo " (car x) y@point{} z)
---------- Buffer: foo ----------
@end group
@end example
@end deffn

@deffn Command backward-sexp &optional arg
This function moves backward across @var{arg} (default 1) balanced expressions.
@end deffn

@deffn Command beginning-of-defun &optional arg
This function moves back to the @var{arg}th beginning of a defun.  If
@var{arg} is negative, this actually moves forward, but it still moves
to the beginning of a defun, not to the end of one.  @var{arg} defaults
to 1.
@end deffn

@deffn Command end-of-defun &optional arg
This function moves forward to the @var{arg}th end of a defun.  If
@var{arg} is negative, this actually moves backward, but it still moves
to the end of a defun, not to the beginning of one.  @var{arg} defaults
to 1.
@end deffn

@defopt defun-prompt-regexp
If non-@code{nil}, this buffer-local variable holds a regular
expression that specifies what text can appear before the
open-parenthesis that starts a defun.  That is to say, a defun begins
on a line that starts with a match for this regular expression,
followed by a character with open-parenthesis syntax.
@end defopt

@defopt open-paren-in-column-0-is-defun-start
If this variable's value is non-@code{nil}, an open parenthesis in
column 0 is considered to be the start of a defun.  If it is
@code{nil}, an open parenthesis in column 0 has no special meaning.
The default is @code{t}.
@end defopt

@defvar beginning-of-defun-function
If non-@code{nil}, this variable holds a function for finding the
beginning of a defun.  The function @code{beginning-of-defun}
calls this function instead of using its normal method.
@end defvar

@defvar end-of-defun-function
If non-@code{nil}, this variable holds a function for finding the end of
a defun.  The function @code{end-of-defun} calls this function instead
of using its normal method.
@end defvar

@node Skipping Characters
@comment  node-name,  next,  previous,  up
@subsection Skipping Characters
@cindex skipping characters

  The following two functions move point over a specified set of
characters.  For example, they are often used to skip whitespace.  For
related functions, see @ref{Motion and Syntax}.

These functions convert the set string to multibyte if the buffer is
multibyte, and they convert it to unibyte if the buffer is unibyte, as
the search functions do (@pxref{Searching and Matching}).

@defun skip-chars-forward character-set &optional limit
This function moves point in the current buffer forward, skipping over a
given set of characters.  It examines the character following point,
then advances point if the character matches @var{character-set}.  This
continues until it reaches a character that does not match.  The
function returns the number of characters moved over.

The argument @var{character-set} is a string, like the inside of a
@samp{[@dots{}]} in a regular expression except that @samp{]} does not
terminate it, and @samp{\} quotes @samp{^}, @samp{-} or @samp{\}.
Thus, @code{"a-zA-Z"} skips over all letters, stopping before the
first nonletter, and @code{"^a-zA-Z"} skips nonletters stopping before
the first letter.  See @xref{Regular Expressions}.  Character classes
can also be used, e.g. @code{"[:alnum:]"}.  See @pxref{Char Classes}.

If @var{limit} is supplied (it must be a number or a marker), it
specifies the maximum position in the buffer that point can be skipped
to.  Point will stop at or before @var{limit}.

In the following example, point is initially located directly before the
@samp{T}.  After the form is evaluated, point is located at the end of
that line (between the @samp{t} of @samp{hat} and the newline).  The
function skips all letters and spaces, but not newlines.

@example
@group
---------- Buffer: foo ----------
I read "@point{}The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
@end group

@group
(skip-chars-forward "a-zA-Z ")
     @result{} nil

---------- Buffer: foo ----------
I read "The cat in the hat@point{}
comes back" twice.
---------- Buffer: foo ----------
@end group
@end example
@end defun

@defun skip-chars-backward character-set &optional limit
This function moves point backward, skipping characters that match
@var{character-set}, until @var{limit}.  It is just like
@code{skip-chars-forward} except for the direction of motion.

The return value indicates the distance traveled.  It is an integer that
is zero or less.
@end defun

@node Excursions
@section Excursions
@cindex excursion

  It is often useful to move point ``temporarily'' within a localized
portion of the program, or to switch buffers temporarily.  This is
called an @dfn{excursion}, and it is done with the @code{save-excursion}
special form.  This construct initially remembers the identity of the
current buffer, and its values of point and the mark, and restores them
after the completion of the excursion.

  The forms for saving and restoring the configuration of windows are
described elsewhere (see @ref{Window Configurations}, and @pxref{Frame
Configurations}).

@defspec save-excursion body@dots{}
@cindex mark excursion
@cindex point excursion
The @code{save-excursion} special form saves the identity of the current
buffer and the values of point and the mark in it, evaluates
@var{body}, and finally restores the buffer and its saved values of
point and the mark.  All three saved values are restored even in case of
an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}).

The @code{save-excursion} special form is the standard way to switch
buffers or move point within one part of a program and avoid affecting
the rest of the program.  It is used more than 4000 times in the Lisp
sources of Emacs.

@code{save-excursion} does not save the values of point and the mark for
other buffers, so changes in other buffers remain in effect after
@code{save-excursion} exits.

@cindex window excursions
Likewise, @code{save-excursion} does not restore window-buffer
correspondences altered by functions such as @code{switch-to-buffer}.
One way to restore these correspondences, and the selected window, is to
use @code{save-window-excursion} inside @code{save-excursion}
(@pxref{Window Configurations}).

The value returned by @code{save-excursion} is the result of the last
form in @var{body}, or @code{nil} if no body forms were given.

@example
@group
(save-excursion @var{forms})
@equiv{}
(let ((old-buf (current-buffer))
      (old-pnt (point-marker))
@end group
      (old-mark (copy-marker (mark-marker))))
  (unwind-protect
      (progn @var{forms})
    (set-buffer old-buf)
@group
    (goto-char old-pnt)
    (set-marker (mark-marker) old-mark)))
@end group
@end example
@end defspec

  @strong{Warning:} Ordinary insertion of text adjacent to the saved
point value relocates the saved value, just as it relocates all markers.
More precisely, the saved value is a marker with insertion type
@code{nil}.  @xref{Marker Insertion Types}.  Therefore, when the saved
point value is restored, it normally comes before the inserted text.

  Although @code{save-excursion} saves the location of the mark, it does
not prevent functions which modify the buffer from setting
@code{deactivate-mark}, and thus causing the deactivation of the mark
after the command finishes.  @xref{The Mark}.

@node Narrowing
@section Narrowing
@cindex narrowing
@cindex restriction (in a buffer)
@cindex accessible portion (of a buffer)

  @dfn{Narrowing} means limiting the text addressable by Emacs editing
commands to a limited range of characters in a buffer.  The text that
remains addressable is called the @dfn{accessible portion} of the
buffer.

  Narrowing is specified with two buffer positions which become the
beginning and end of the accessible portion.  For most editing commands
and most Emacs primitives, these positions replace the values of the
beginning and end of the buffer.  While narrowing is in effect, no text
outside the accessible portion is displayed, and point cannot move
outside the accessible portion.

  Values such as positions or line numbers, which usually count from the
beginning of the buffer, do so despite narrowing, but the functions
which use them refuse to operate on text that is inaccessible.

  The commands for saving buffers are unaffected by narrowing; they save
the entire buffer regardless of any narrowing.

@deffn Command narrow-to-region start end
This function sets the accessible portion of the current buffer to start
at @var{start} and end at @var{end}.  Both arguments should be character
positions.

In an interactive call, @var{start} and @var{end} are set to the bounds
of the current region (point and the mark, with the smallest first).
@end deffn

@deffn Command narrow-to-page &optional move-count
This function sets the accessible portion of the current buffer to
include just the current page.  An optional first argument
@var{move-count} non-@code{nil} means to move forward or backward by
@var{move-count} pages and then narrow to one page.  The variable
@code{page-delimiter} specifies where pages start and end
(@pxref{Standard Regexps}).

In an interactive call, @var{move-count} is set to the numeric prefix
argument.
@end deffn

@deffn Command widen
@cindex widening
This function cancels any narrowing in the current buffer, so that the
entire contents are accessible.  This is called @dfn{widening}.
It is equivalent to the following expression:

@example
(narrow-to-region 1 (1+ (buffer-size)))
@end example
@end deffn

@defspec save-restriction body@dots{}
This special form saves the current bounds of the accessible portion,
evaluates the @var{body} forms, and finally restores the saved bounds,
thus restoring the same state of narrowing (or absence thereof) formerly
in effect.  The state of narrowing is restored even in the event of an
abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}).
Therefore, this construct is a clean way to narrow a buffer temporarily.

The value returned by @code{save-restriction} is that returned by the
last form in @var{body}, or @code{nil} if no body forms were given.

@c Wordy to avoid overfull hbox.  --rjc 16mar92
@strong{Caution:} it is easy to make a mistake when using the
@code{save-restriction} construct.  Read the entire description here
before you try it.

If @var{body} changes the current buffer, @code{save-restriction} still
restores the restrictions on the original buffer (the buffer whose
restrictions it saved from), but it does not restore the identity of the
current buffer.

@code{save-restriction} does @emph{not} restore point and the mark; use
@code{save-excursion} for that.  If you use both @code{save-restriction}
and @code{save-excursion} together, @code{save-excursion} should come
first (on the outside).  Otherwise, the old point value would be
restored with temporary narrowing still in effect.  If the old point
value were outside the limits of the temporary narrowing, this would
fail to restore it accurately.

Here is a simple example of correct use of @code{save-restriction}:

@example
@group
---------- Buffer: foo ----------
This is the contents of foo
This is the contents of foo
This is the contents of foo@point{}
---------- Buffer: foo ----------
@end group

@group
(save-excursion
  (save-restriction
    (goto-char 1)
    (forward-line 2)
    (narrow-to-region 1 (point))
    (goto-char (point-min))
    (replace-string "foo" "bar")))

---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo@point{}
---------- Buffer: foo ----------
@end group
@end example
@end defspec

@ignore
   arch-tag: 56e8ff26-4ffe-4832-a141-7e991a2d0f87
@end ignore