Many of the more complicated Emacs commands include their own sets of help keystrokes. These commands often have their own help functionality, but help is invoked with ? rather than the standard help key. Here is a summary of some popular complex commands and what ? does within each of them:
You see a list of the most frequently used commands in the minibuffer. This list is far from complete. Type C-h m (for describe-mode) for more comprehensive documentation and C-h b (for describe-bindings) for all the key bindings available to you.
You see a *Help*
window listing the available commands. Typing C-h does the same thing. This also works with
query-replace-regexp.
Behavior is similar to query-replace just described.
You see a *Help*
window giving information on
buffer menu mode. This command has the same effect as typing
C-h m (for describe-mode).
When you are responding to a minibuffer prompt with the name of
something on which Emacs can do completion, typing ? at any time gives you a
*Completions*
window with the choices available at
that point. Completion is explained in detail later in this chapter.