The minibuffer has its own set of local keymaps; they contain various completion and exit commands.
minibuffer-local-map is used for ordinary input (no completion).
minibuffer-local-ns-map is similar, except that SPC exits
just like RET.
minibuffer-local-completion-map is for permissive completion.
minibuffer-local-must-match-map is for strict completion and
for cautious completion.
minibuffer-local-filename-completion-map is like the two
previous ones, but specifically for file name completion.
It does not bind SPC.
By default, TAB, SPC and ? do completion in
minibuffer-local-completion-map. If you commonly complete over
collections that have elements with space or question mark characters in
them, it may be convenient to disable completion on those keys by
putting this in your init file:
(keymap-set minibuffer-local-completion-map "SPC" 'self-insert-command) (keymap-set minibuffer-local-completion-map "?" 'self-insert-command)