This function switches to another "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 meta1-[ META3_CHARACTER binds this function to ^[[. You may then bind meta key sequences with either of the two following formats: bind ^[[A BACKWARD_HISTORY or bind META3-A BACKWARD_HISTORY Works just like the META1_CHARACTER and the META2_CHARACTER but the default binding is meta1-[ which is very useful for binding arrow keys and other escape sequences.