Final documentation tweaks.

* etc/NEWS: Update the NEWS entry.

* src/xdisp.c (syms_of_xdisp): Mention the fact that restrictions
may be locked around 'fontification-functions'.

2 files changed, 13 insertions, 8 deletions

diff --git a/etc/NEWS b/etc/NEWS
index ec6f6c7168a..8d958c66cd8 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -337,13 +337,13 @@ Use something like 'M-x shell RET ssh <host> RET' instead.
 ** Emacs is now capable of editing files with arbitrarily long lines.
 The display of long lines has been optimized, and Emacs no longer
 chokes when a buffer on display contains long lines.  If you still
-experience slowdowns while editing files with long lines, this is
-either due to font locking, which you can turn off with M-x
-font-lock-mode or C-u C-x x f, or to the current major mode or one of
-the enabled minor modes, in which case you should open the the file
-with M-x find-file-literally instead of C-x C-f.  The variable
-'long-line-threshold' controls whether and when these display
-optimizations are used.
+experience slowdowns while editing files with long lines, this is due
+either to the current major mode or one of the enabled minor modes, in
+which case you should open the the file with M-x find-file-literally
+instead of C-x C-f, or to truncation of long lines, which you can
+disable with C-x x t.  The buffer may also be occasionally
+mis-fontified.  The variable 'long-line-threshold' controls whether
+and when these display optimizations are used.
 
 +++
 ** New command to change the font size globally.
diff --git a/src/xdisp.c b/src/xdisp.c
index d91a7ac65bb..8867406c4e2 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -36653,7 +36653,12 @@ The tool bar style must also show labels for this to have any effect, see
     doc: /* List of functions to call to fontify regions of text.
 Each function is called with one argument POS.  Functions must
 fontify a region starting at POS in the current buffer, and give
-fontified regions the property `fontified'.  */);
+fontified regions the property `fontified'.
+
+Note that, when the buffer contains one or more lines whose length is
+above `long-line-threshold', the restrictions of the buffer are locked
+(see `narrow-to-region'), and these functions only have access to a
+small portion of the buffer around POS.  */);
   Vfontification_functions = Qnil;
   Fmake_variable_buffer_local (Qfontification_functions);