What is the select word/symbol function bound to <double-mouse-1>

Question

I love the ability to select word/symbol at point which I currently do with double mouse click. I would like to be able to do it from the keyboard, and so I'd like to bind it to a keystroke (or maybe it already is?), so I need the name of the function. I assume the function must already exist, but I cannot figure out what it's name is.

I tried C-h k but then when I double click the mouse the help for <down-mouse-1> shows up (I assume the help system doesn't wait for the second click or something). I also searched the documentation where this functionality is defined in section 21.2, but it does not say the name of the function.

Update: For typical keybinding I suppose it is the equivalent to <C-left> followed by <C-S-right> which are left-word and right-word respectively, although the shift key is held for the latter. (I do not fully understand the relationship between keyboard designations with the shift key and their mapping to functions, the help for <C-S-right> translates it to <C-right> before it identifies it as right-word)

Answer 1

It's actually a bit complicated. When you double-click mouse-1 there are multiple actions. <down-mouse-1> occurs first, when you press the button. Then mouse-1 occurs, when you release the button.

<down-mouse-1> is bound to command mouse-drag-region, and that command calls mouse-drag-track. That function counts the mouse-button clicks and keeps track of any mouse movement (if you double-click that means that you did not move the mouse).

mouse-drag-track calls function mouse-start-end to determine the range of text to select. It passes to mouse-start-end the position where you clicked for, the first two args, and the click count, as the third arg. This is mouse-start-end:

mouse-start-end is a compiled Lisp function in `mouse.el'.

(mouse-start-end START END MODE)

Return a list of region bounds based on START and END according to MODE.
If MODE is 0 then set point to (min START END), mark to (max START END).
If MODE is 1 then set point to start of word at (min START END),
mark to end of word at (max START END).
If MODE is 2 then do the same for lines.

The click-count passed as the third arg (MODE) is 1 for a double-click.

You won't be able to just call some of this code from a keyboard key sequence, but examining the code might help you write a keyboard key-bindable command to do what you want.

Answer 2

@Drew has explained some of the complexity associated with events bound to mouse actions. As for your ultimate goal of marking the word at point using the keyboard, you might be interested in expand-region.

expand-region allows you to manipulate the region by semantic units. For example, when no region is active, calling er/expand-region (typically bound to C-=) will mark the current word. Calling it again expands the region to the current sentence. And then the paragraph, section etc. The actual units will depend on the mode you're in, so in lisp modes they would be symbol, expression enclosing the symbol, expression enclosing that expression etc.

The linked page has further explanation and a video demonstrating this.

Answer 3

Here's a function that I extracted from mouse-set-region that does the marking when you double click:

(defun ora-mark-like-double-mouse-1 ()
  (interactive)
  (let ((bnd (mouse-start-end (point) (point) 1)))
    (goto-char (car bnd))
    (push-mark)
    (set-mark (point))
    (goto-char (cadr bnd))))