In TTX filter: DF tags across external UT cause problem when merging back

[Former user]

Original issue 158 created by @ysavourel on 2010-12-29T13:23:33.000Z:

When a <df> element is used across external code, its closing tag may get moved out of place when resolving inline codes.

The filter needs to close and re-open the <df> elements when crossing external code.

[Former user]

Comment [1.](https://code.google.com/p/okapi/issues/detail?id=158#c1) originally posted by @ysavourel on 2011-07-29T04:06:08.000Z:

issue \#174 has been merged into this issue.