Preferences option
Shell.Options.Preferences
val externalEditorCommand: string option
Specifies the command you prefer to use to invoke a one-shot external editor. This option has an effect only if the editor option is set to "External", meaning that you wish to use a one-shot external editor.
On UNIX, the default is
"xterm -name VIsual -e vi +%l %f"
On Windows it is
"C:\\Program Files\Accessories\Wordpad"
This value of this option appears, and can be set, in the External Editor text box on the GUI environment's Preferences > Editor dialog.