Add FIXME comment.

diff --git a/src/doc.c b/src/doc.c
index d27fa3f792d5a80d95414fb37fefac334c9496c6..3832eb3708d6e31536f8bc6a3dfa63bae8e12f3d 100644 (file)
--- a/src/doc.c
+++ b/src/doc.c
@@ -347,6 +347,8 @@ string is passed through `substitute-command-keys'.  */)
     {
       if (XSUBR (fun)->doc == 0)
        return Qnil;
+      /* FIXME: This is not portable, as it assumes that string
+        pointers have the top bit clear.  */
       else if ((EMACS_INT) XSUBR (fun)->doc >= 0)
        doc = build_string (XSUBR (fun)->doc);
       else