Document that {en,de}code-coding-string preserve match data

* lisp/international/mule.el (define-coding-system):
Require :pre-write-conversion and :post-read-conversion functions
to leave the match data untouched.
* src/coding.c (Fdecode_coding_string, Fencode_coding_string):
Document functions as match-data-preserving.

Suggested by Stefan Monnier (see bug#41445).

1 files changed, 2 insertions, 2 deletions

diff --git a/src/coding.c b/src/coding.c
index 34f36d5a86a..071124b4ef1 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -10395,7 +10395,7 @@ representation of the decoded text.
 
 This function sets `last-coding-system-used' to the precise coding system
 used (which may be different from CODING-SYSTEM if CODING-SYSTEM is
-not fully specified.)  */)
+not fully specified.)  The function does not change the match data.  */)
   (Lisp_Object string, Lisp_Object coding_system, Lisp_Object nocopy, Lisp_Object buffer)
 {
   return code_convert_string (string, coding_system, buffer,
@@ -10415,7 +10415,7 @@ case, the return value is the length of the encoded text.
 
 This function sets `last-coding-system-used' to the precise coding system
 used (which may be different from CODING-SYSTEM if CODING-SYSTEM is
-not fully specified.)  */)
+not fully specified.)  The function does not change the match data.  */)
   (Lisp_Object string, Lisp_Object coding_system, Lisp_Object nocopy, Lisp_Object buffer)
 {
   return code_convert_string (string, coding_system, buffer,