Variable: completing-read-function
completing-read-function is a variable defined in minibuffer.el.gz.
Value
completing-read-default
Documentation
The function called by completing-read to do its work.
It should accept the same arguments as completing-read.
Probably introduced at or before Emacs version 24.1.
Source Code
;; Defined in /usr/src/emacs/lisp/minibuffer.el.gz
(defvar completing-read-function #'completing-read-default
"The function called by `completing-read' to do its work.
It should accept the same arguments as `completing-read'.")