Re: display.texi: (<line>,<col>) isn't documented.

[Richard Stallman]

    Quick, select 50 characters starting...there. You might use the keyboard to
    place the cursor and then use `C-u 50', but you might instead just grab the
    mouse, drag, and stop when the size is 50.

If you want to "select 50 characters" you should use keyboard chars.
The mouse is the wrong tool for the job.