Keyboard Devices/System
The editor mostly stays in a GetKey()/PutKey() loop.  The putkey portion is 
where keys are acted-upon.  TempleOS has a chain of putkey hndlrs in a 
Circular Queue with priorities.  The highest priority hndlrs can choose to 
terminate handling, otherwise, the keys get sent on down the chain.

KeyDevAdd() defines a putkey device with a priority.  "Device" might be a 
misnomer.  Currently, the following are defined:

Priority    Hndlr
---------- ---------
0x20000000 MyPutKey() user hndlr
0x40000000 KDInputFilterPutKey() for In(), InStr(), and InFile() handling.
0x60000000 KDRawPutKey() nonwindowed direct to video mem debug output. 
0x80000000 KDDocPutKey() standard document cmds

Since handling individual keys is slow, TempleOS supports PutS() as well.  If no 
puts hndlr is defined, individual keys are sent.

CDoc.user_put_key and CDoc.user_put_s are call back routines which offer some 
neat tricks.  See ::/Apps/Psalmody/JukeBox.HC.  There is a var CDoc.user_put_dat
a which gets passed to them.

CtrlAltCBSet        Funct Set callback for <CTRL-ALT-letter>.
KeyDescSet          Funct Call this from key hndlr to report desc in KeyMap().
KeyDevAdd           Funct Places hook in StdOut chain. See Keyboard Devices.
KeyDevRem           Funct Remove StdOut hook and free.