The minibuffer is an Emacs buffer, albeit a peculiar one, and the usual Emacs commands are available for editing the argument text. (The prompt, however, is read-only, and cannot be changed.)
Since RET in the minibuffer submits the argument, you can’t
use it to insert a newline. You can do that with C-q C-j, which
inserts a C-j control character, which is formally equivalent to
a newline character (see Inserting Text). Alternatively, you can
use the C-o (open-line) command (see Blank Lines).
Inside a minibuffer, the keys TAB, SPC, and ? are often bound to completion commands, which allow you to easily fill in the desired text without typing all of it. See Completion. As with RET, you can use C-q to insert a TAB, SPC, or ‘?’ character. If you want to make SPC and ? insert normally instead of starting completion, you can put the following in your init file:
(keymap-unset minibuffer-local-completion-map "SPC") (keymap-unset minibuffer-local-completion-map "?")
For convenience, C-a (move-beginning-of-line) in a
minibuffer moves point to the beginning of the argument text, not the
beginning of the prompt. For example, this allows you to erase the
entire argument with C-a C-k.
When the minibuffer is active, the echo area is treated much like an ordinary Emacs window. For instance, you can switch to another window (with C-x o), edit text there, then return to the minibuffer window to finish the argument. You can even kill text in another window, return to the minibuffer window, and yank the text into the argument. There are some restrictions on the minibuffer window, however: for instance, you cannot split it. See Multiple Windows.
Normally, the minibuffer window occupies a single screen line.
However, if you add two or more lines’ worth of text into the
minibuffer, it expands automatically to accommodate the text. The
variable resize-mini-windows controls the resizing of the
minibuffer. The default value is grow-only, which means the
behavior we have just described. If the value is t, the
minibuffer window will also shrink automatically if you remove some
lines of text from the minibuffer, down to a minimum of one screen
line. If the value is nil, the minibuffer window never changes
size automatically, but you can use the usual window-resizing commands
on it (see Multiple Windows).
The variable max-mini-window-height controls the maximum
height for resizing the minibuffer window. A floating-point number
specifies a fraction of the frame’s height; an integer specifies the
maximum number of lines; nil means do not resize the minibuffer
window automatically. The default value is 0.25.
The C-M-v command in the minibuffer scrolls the help text from commands that display help text of any sort in another window. You can also scroll the help text with M-PageUp and M-PageDown (or, equivalently, M-prior and M-next). This is especially useful with long lists of possible completions. See Using Other Windows.
Emacs normally disallows most commands that use the minibuffer while
the minibuffer is active. To allow such commands in the minibuffer,
set the variable enable-recursive-minibuffers to t.
You might need also to enable minibuffer-depth-indicate-mode
to show the current recursion depth in the minibuffer prompt
on recursive use of the minibuffer.
When active, the minibuffer is usually in minibuffer-mode.
This is an internal Emacs mode without any special features.
When not active, the minibuffer is in minibuffer-inactive-mode,
and clicking mouse-1 there shows the *Messages* buffer.
If you use a dedicated frame for minibuffers, Emacs also recognizes
certain keys there, for example, n to make a new frame.