Usage: BIND <key> META2_CHARACTER
  This function switches to an "alternate" keymap.  That is,
  after this character is hit, the next key hit can have a new
  definition.  This is how the Escape sequences are done.  In
  fact, the escape key's default binding is META1_CHARACTER.  For
  example:
    BIND ^X META2_CHARACTER
  binds this function to ^X.  You may then bind meta key
  sequences with either of the two following formats:
    BIND ^X? HELP_CHARACTER
  or
    BIND META2-? HELP_CHARACTER
