frame, it is hard to select the one the user intended. Also, if the
buffer is read only, we don't want to accept a drop there. So
currently
I'd argue that we want to accept the drop (and then signal an error).
Just like C-y is accepted (i.e. the yank function is invoked) but then
signals an error.
Now that I think about it, rather than an alist, we might just want to
make
the drop into an event that we look up in the keymaps. If the drop is
in
the tool-bar or the menu-bar, the event generated should be different
so
that we can bind it to a different command (just like [mouse-1] turns
into
[mode-line mouse-1] when clicking on the mode-line).