Prompt with PROMPT.
Optional second arg DEF is value to return if user enters an empty line.
If DEF is a list of default values, return its first element.
-If optional third arg REQUIRE-MATCH is non-nil,
- only existing buffer names are allowed.
+Optional third arg REQUIRE-MATCH determines whether non-existing
+ buffer names are allowed. It has the same meaning as the
+ REQUIRE-MATCH argument of `confirm-after-completion'.
The argument PROMPT should be a string ending with a colon and a space.
If `read-buffer-completion-ignore-case' is non-nil, completion ignores
case while reading the buffer name.