I guess you mean the key-binding
You can sort-of answer your question by using
C-h k followed by triple-clicking
mouse-1 (the first/left mouse button).
This is what I see when I do that in the Emacs 26 pretest:
<mouse-1> (translated from
<triple-mouse-1>) at that spot runs the
mouse-set-point (found in
global-map), which is an interactive
compiled Lisp function in
It is bound to
(mouse-set-point EVENT &optional PROMOTE-TO-REGION)
Move point to the position clicked on with the mouse.
This should be bound to a mouse click event type.
PROMOTE-TO-REGION is non-
nil and event is a multiple-click, select
the corresponding element around point, with the resulting position of
point determined by
In Emacs prior to Emacs 26 you also see the doc for the button-down event,
To figure out what's happening you need to check the code of
mouse-set-point. You'll see that when called interactively its second arg,
PROMOTE-TO-REGION, is non-
nil (coming from the numeric prefix arg). So it calls
mouse-set-region then calls
(1- click-count), where
click-count is the number of clicks. For a triple-click it thus passes
Finally, given the value
2 as its
MODE argument, function
mouse-start-end selects the whole line. Its doc string (
C-h f mouse-start-end) tells you:
mouse-start-end is a compiled Lisp function in
(mouse-start-end START END MODE)
Return a list of region bounds based on
END according to
MODE is 0 then set point to
(min START END), mark to
(max START END).
MODE is 1 then set point to start of word at
(min START END),
mark to end of word at
(max START END).
MODE is 2 then do the same for lines.
Whew! Not so easy, but Emacs finally tells you what you wanted to know. It is (ultimately) function
mouse-start-end that selects the whole line. But it does that only because of the
MODE parameter passed to it from
mouse-set-region only does the right thing because of code that is in
mouse.elcode is a bit convoluted, in part because the Emacs mouse does a lot of different things with the same buttons. If you want a command that does only what triple-clicking
mouse-1does then you (or someone else) will need to dig into that code and compose bits of it (or similar or write code from scratch) to do the job.
interactivespec. Check the manual.