runtime(doc): clarify 'fileignorecase' option setting

fixes: #18360

Signed-off-by: Christian Brabandt <cb@256bit.org>

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index e1361d34d65c6ea1f3c32f16d4ff01f48c4fd722..445e925c3564d05d41e7d9fe34b44af67c085c49 100644 (file)
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3791,7 +3791,13 @@ A jump table for the options with a short description can be found at |Q_op|.
 'fileignorecase' 'fic' boolean (default on for systems where case in file
                                 names is normally ignored)
                        global
-       When set case is ignored when using file names and directories.
+       When set, case is ignored when using file and directory names.
+
+       This option is on by default on systems where the filesystem is
+       traditionally case-insensitive (for example MS-Windows and macOS).
+       However, Vim cannot determine at runtime whether a particular
+       filesystem is case-sensitive or case-insensitive.
+
        See 'wildignorecase' for only ignoring case when doing completion.
 
                                        *'filetype'* *'ft'*