Doc clarificationscratch/string-common-prefix

2 files changed, 3 insertions, 2 deletions

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index 0447b2262cd..ae77b4e3a2d 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -254,7 +254,7 @@ properties removed.
 This function returns the longest initial substring common to all
 members of @var{collection}.  It returns an empty string if there is no
 common prefix or if @var{collection} is @code{nil}.  If @var{collection}
-contains exactly one string, it returns that string.
+contains (after filtering) exactly one string, it returns that string.
 
 @example
 (string-common-prefix '("foobar" "foozot"))
diff --git a/lisp/subr.el b/lisp/subr.el
index 60ea8ca4148..68f9d6b37cc 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -6006,7 +6006,8 @@ attention to letter-case differences."
   "Return the longest common prefix from a COLLECTION of strings.
 
 Return \"\" if there is no common prefix or if COLLECTION is nil.
-If COLLECTION contains exactly one string, return that string.
+If COLLECTION contains (after filtering) exactly one string, return
+that string.
 
 If IGNORE-CASE is non-nil, letter case is ignored when matching the
 substrings, but no guarantee is made about the letter-case of the return