* lisp/minibuffer.el (read-file-name): Note that the semantics of
INITIAL are odd (bug#37883).
- anything else behaves like t except that typing RET does not exit if it
does non-null completion.
-Fifth arg INITIAL specifies text to start with.
+Fifth arg INITIAL specifies text to start with. It will be
+interpreted as the trailing part of DEFAULT-FILENAME, so using a
+full file name for INITIAL will usually lead to surprising
+results.
Sixth arg PREDICATE, if non-nil, should be a function of one
argument; then a file name is considered an acceptable completion