Hi Hard Off,

That would be sufficiently simple --

But maybe I'm missing something, because I understand that [key] reads the keyboard's input, then [receive] and [send] can pipe values around within PD, and a Bang does all sorts of things within PD.

However, I don't understand how any combination of those things will "emulate" the pressing of a keyboard key.

Here's an example of what I'm trying to do:

Ableton Live is the currently active window, PD is in the background.  (PD is already working beautifully as a MIDI transformer.)

PD receives a MIDI message from an external MIDI controller (and, of course, it doesn't have to be in focus to do so.)  When it gets the MIDI message, it sends out a sequence of keystrokes -- just as if these keystrokes were being typed into the keyboard.

Since, on the OS level, the currently active window receives any keystroke messages, the Ableton Live window will receive them -- just as if they had been typed into the keyboard.

Thanks for any more thoughts!
rs