Variable: show-help-function
show-help-function is a variable defined in keyboard.c.
Value
tooltip-show-help
Documentation
If non-nil, the function that implements the display of help.
It's called with one argument, the help string to display.
Probably introduced at or before Emacs version 21.1.
Source Code
// Defined in /usr/src/emacs/src/keyboard.c
DEFVAR_LISP ("show-help-function", Vshow_help_function,
doc: /* If non-nil, the function that implements the display of help.
It's called with one argument, the help string to display. */);