key_prefix

      key: <string>

 If you specify a key using this command, you can no longer bind to this key.
 You can however, use it as the first key in a 2-key key binding.

 eg:  key_prefix "^K"
      key_bind   "^K ^V"  "block_delete other_undelete"

 This sets ^K ^V to do a block move.

 Only special keys (ie: non alphanumeric or ASCII keys) may be specified.
 Ctrl-Break and Esc cannot be bound to. To name a key use its standard name
 (eg: PgDn for page down).

 A list of valid key names is given in the Keys reference.