RE: can a command specify overwrite selection behavior?

[Drew Adams]

> Drew, what i didn't understand is why the insert-date property makes a
> distinction on whether a command is called by name or by a keyboard
> shortcut?

Ah, good question.  Here's the answer:

(defun delete-selection-pre-hook ()
  (when (and delete-selection-mode
             transient-mark-mode mark-active
               (not buffer-read-only))
    (let ((type (and (symbolp this-command)
                         (get this-command ; <=======
                          'delete-selection))))

If you debug this (use `message', not `debug-on-entry'!), you'll see that when
you use `M-x' the value of `this-command' is `execute-extended-command', not
`insert-date'.  And `execute-extended-command' does not have a non-nil
`delete-selection' property.

`execute-extended-command' is a bit special wrt `this-command' and
`last-command'.  It DTRT in the end, essentially removing itself from the party,
but that's only at the end.  While `execute-extended-command' is executing, it
is the value of `this-command'.

People sometimes get thrown off by this kind of thing, and similar things wrt
`M-:' (and `C-x C-e', `C-M-x'...).

The thing to remember is that `M-x' and `M-:' are themselves keys that are bound
to commands, and that even though they invoke or evaluate other stuff (and that
other stuff is what we focus on), that is not the same as just invoking or
evaluating the other stuff directly.  They add their bit to the mix, and
sometimes that makes a difference.

It can help to remember that EVERYTHING in Emacs is a COMMAND.  Or, rather,
every user interaction is via a command.  Outside Emacs we are not used to
thinking that way (because outside Emacs it is not true).  But even when you hit
a letter key such as `g' Emacs invokes a command (by default,
`self-insert-command').

Always.  Well no, you can undefine keys: (global-unset-key "a") etc., but as a
general rule it is true.

(I know that you know all of this, but I find it's worth reminding myself from
time to time.  Emacs interaction is all about commands.)