OS X key bindings on Shift-Tab

I'm curious as to why I need to use "EM" to define a key binding on  
OS X for shift tab:

#+cocoa
(editor:bind-key "Indent Form" #\EM :mode "Lisp") ;shift-tab
#-cocoa
(editor:bind-key "Indent Form" "Shift-Tab" :mode "Lisp")

If I try to use "Shift-Tab" on the Mac, I get an editor message  
"Undefined command EM".

What is "EM"?




John DeSoi, Ph.D.
http://pgedit.com/
Power Tools for PostgreSQL