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 META1_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 META1-? HELP_CHARACTER