RE: Binding a command to the down-event of a toolbar button

[Drew Adams]

    >> Is such behavior normal in tool bars in other user interfaces?
    >> If not, I think we should not do it.

Why not? It's often good to stick to "normal", "standard", or common UI
features so that users know what to expect. But what's the harm in providing
functionality where the common UIs have none? Users of common UIs won't
think to try press-and-hold or mouse-3 on a tool-bar icon, and they won't be
shocked by the possibility.

    I use Emacs's tool-bar as a "control bar", so its behavior
    doesn't need to
    be related to what people are usually accumstomed for tool-bars.
    See http://www.iro.umontreal.ca/~monnier/elisp/mpc.png for a snapshot.

Looks good to me.
BTW - The pause symbol usually has vertical, not horizontal bars.

    I'd like to be able to also offer the
    press-and-hold behavior
    which may be more convenient in other situations.

Yes, why not?

    I think my request for down-events on the tool-bar is related
    to some other people's requests to be able to bind different
    actions for mouse-1, mouse-2, mouse-3.

Yes, why not? (I was one of the "other people", for the same reason: why
not?)

Why limit Emacs, even if it is not common for GUIs to use other mouse keys
or press-and-hold on tool-bar icons? Tool bars are not all that useful
anyway - why not see if Emacs developers and users can improve on this
not-so-useful cliche? At one time even menus and mice were crazy
experiments.

IOW, it wouldn't hurt to open up the feature set here, and allow for some
invention. There is nothing sacrosanct about the dominant UIs. If using
press-and-hold with a tool bar turns out to be not very useful, that will
soon become apparent and that potential feature will remain unused. If it
turns out to be useful in some contexts, then we will have gained by
allowing the possibility.

Think of the Emacs mouse functionality (e.g. mouse-3 to extend selection,
mouse-2 to paste). If we respected the "norm" then we would have the same
brain-dead mouse as most apps.  Emacs can always do better, precisely
because it is open to experimentation by users. Let a hundred flowers bloom.