chain-to-keymap in keymap%

Chains a keymap off this one.

Multiple keymaps can be chained off one keymap using chain-to-keymap. When keymaps are chained off a main keymap, events not handled by the main keymap are passed to the chained keymaps until some chained keymap handles the events. Keymaps can be chained together in an arbitrary acyclic graph.

Keymap chaining is useful because multiple-event sequences are handled correctly for chained groups. Without chaining, a sequence of events can produce state in a keymap that must be reset when a callback is invoked in one of the keymaps. This state can be manually cleared with break-sequence, though calling the break-sequence method also invokes the handler installed by set-break-sequence-callback.

• (send a-keymap chain-to-keymap next prefix?) -> void
     next : keymap% object
     prefix? : boolean

  The next keymap will be used to handle events which are not handled by this keymap. If prefix? is a true value, then next will take precedence over other keymaps already chained to this one.