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Searching the Active Keymaps

Here is a pseudo-Lisp summary of how Emacs searches the active keymaps:

(or (if overriding-terminal-local-map
        (find-in overriding-terminal-local-map))
    (if overriding-local-map
        (find-in overriding-local-map)
      (or (find-in (get-char-property (point) 'keymap))
          (find-in-any emulation-mode-map-alists)
          (find-in-any minor-mode-overriding-map-alist)
          (find-in-any minor-mode-map-alist)
          (if (get-text-property (point) 'local-map)
              (find-in (get-char-property (point) 'local-map))
            (find-in (current-local-map)))))
    (find-in (current-global-map)))

Here, find-in and find-in-any are pseudo functions that search in one keymap and in an alist of keymaps, respectively. Note that the set-transient-map function works by setting overriding-terminal-local-map (see Controlling Active Maps).

In the above pseudo-code, if a key sequence starts with a mouse event (see Mouse Events), that event’s position is used instead of point, and the event’s buffer is used instead of the current buffer. In particular, this affects how the keymap and local-map properties are looked up. If a mouse event occurs on a string embedded with a display, before-string, or after-string property (see Special Properties), and the string has a non-nil keymap or local-map property, that overrides the corresponding property in the underlying buffer text (i.e., the property specified by the underlying text is ignored).

When a key binding is found in one of the active keymaps, and that binding is a command, the search is over—the command is executed. However, if the binding is a symbol with a value or a string, Emacs replaces the input key sequences with the variable’s value or the string, and restarts the search of the active keymaps. See Key Lookup.

The command which is finally found might also be remapped. See Remapping Commands.