ctl-x-map key map has entries of different kind

Question

when i run,

 (dolist (elt ctl-x-map)
             (print elt))

it prints,

#^[nil nil keymap 
#^^[3 0 pop-global-mark nil list-buffers save-buffers-kill-terminal list-directory eval-last-sexp find-file nil nil indent-rigidly nil kmacro-keymap downcase-region (keymap (108 . set-language-environment) (99 . universal-coding-system-argument) (28 . set-input-method) (88 . set-next-selection-coding-system) (120 . set-selection-coding-system) (112 . set-buffer-process-coding-system) (107 . set-keyboard-coding-system) (116 . set-terminal-coding-system)
#^^[3 0 pop-global-mark nil list-buffers save-buffers-kill-terminal list-directory eval-last-sexp find-file nil nil indent-rigidly nil kmacro-keymap downcase-region (keymap (108 . set-language-environment) (99 . universal-coding-system-argument) (28 . set-input-method) (88 . set-next-selection-coding-system) (120 . set-selection-coding-system) (112 . set-buffer-process-coding-system) (107 . set-keyboard-coding-system) (116 . set-terminal-coding-system) (70 . set-file-name-coding-system) (114 . revert-buffer-with-coding-system) (102 . set-buffer-file-coding-system)) set-goal-column delete-blank-lines mark-page read-onl
(67108896 . pop-global-mark)

(C-left . previous-buffer)

(left . previous-buffer)

(C-right . next-buffer)

I expected Ctl-x-map to be a plain map with key sequence as key and function name as value (ex - (C-left . previous-buffer)). But the second & third entry that begins with #^^[ proves it to be wrong. Is ctl-x-map variable, some sort of map within a map ?

Answer 1

It is a full keymap, not a sparse keymap. That is, it has an entry that is a char-table.

See the Elisp manual, node Format of Keymaps.

It says this about a char-table entry (emphasis added):

char-table

If an element of a keymap is a char-table, it counts as holding bindings for all character events with no modifier bits (see modifier bits): element n is the binding for the character with code n. This is a compact way to record lots of bindings. A keymap with such a char-table is called a full keymap. Other keymaps are called sparse keymaps.