Keyboard Macros

I would like to  see a modification to the X server to allow me to 
define keyboard macros in the sense that would let me type in various 
"special keys" and have an entire string entered into the "current" 
application.  For example, I might enter <alt><ctrl>s and my signature 
would be entered into the current application. 

AFAICT, this cannot be done so far in X (at least not with the modkey 
utilities -- it appears only one key can be assigned in place of some 
other key).

Am I missing something?

The last time I tried asking the question (under the old mailing list 
structure) the only answer I got was to the effect that it would not be 
<something> with X.  Don't understand why -- can someone elaborate -- 
it certainly cannot be a technical impossibility -- is it an X.org 
proscription?

(I recognize there could be some difficulties -- if the string included 
the characters to change the current application to another we might 
have to think about what to do, or simply prohibit something like that.

Randy Kramer