Fix documentation and tests for 'string-distance'

* src/fns.c (Fstring_distance): Doc fix.

* doc/lispref/strings.texi (Text Comparison): Document
'string-distance'.

* etc/NEWS: Fix wording and mark as documented in the manuals.

* test/src/fns-tests.el (test-string-distance): Move from
subr-tests.el and rename.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/fns.c b/src/fns.c
index 6e851c8555a..1d69f15b0ed 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -155,9 +155,11 @@ If STRING is multibyte, this may be greater than the length of STRING.  */)
 
 DEFUN ("string-distance", Fstring_distance, Sstring_distance, 2, 3, 0,
        doc: /* Return Levenshtein distance between STRING1 and STRING2.
-If BYTECOMPARE is nil, compare character of strings.
-If BYTECOMPARE is t, compare byte of strings.
-Case is significant, but text properties are ignored. */)
+The distance is the number of deletions, insertions, and substitutions
+required to transform STRING1 into STRING2.
+If BYTECOMPARE is nil or omitted, compute distance in terms of characters.
+If BYTECOMPARE is non-nil, compute distance in terms of bytes.
+Letter-case is significant, but text properties are ignored. */)
   (Lisp_Object string1, Lisp_Object string2, Lisp_Object bytecompare)
 
 {