scratch/track-changes f738662f6cf: * doc/lispref/text.texi (Tracking changes): Document the `error` case

[Stefan Monnier]

branch: scratch/track-changes
commit f738662f6cf0bf426999849ed078b277d4d01519
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    * doc/lispref/text.texi (Tracking changes): Document the `error` case
---
 doc/lispref/text.texi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 2875f6f6ba8..2c4262e3b9c 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -6501,6 +6501,14 @@ returned by @var{func}.  But note that @var{func} is 
called just once
 regardless of how many changes occurred: those are summarized into
 a single @var{beg}/@var{end}/@var{before} triplet.
 
+In some cases, the library is not properly notified of all changes,
+for example because of a bug in the low-level C code or because of an
+improper use of @code{inhibit-modification-hooks}.  When it detects such
+a problem, @var{func} receives a @code{@var{beg}..@var{end}} region
+which covers the whole buffer and the @var{before} argument is the
+symbol @code{error} to indicate that the library was unable to determine
+what was changed.
+
 Once @var{func} finishes, @code{track-changes-fetch} re-enables the
 @var{signal} function so that it will be called the next time a change
 occurs.  This is the reason why it calls @var{func} instead of returning