The echo area is used for displaying error messages
(see 错误), for messages made with the message primitive,
and for echoing keystrokes. It is not the same as the minibuffer,
despite the fact that the minibuffer appears (when active) in the same
place on the screen as the echo area. See The
Minibuffer in The GNU Emacs Manual.
Apart from the functions documented in this section, you can print
Lisp objects to the echo area by specifying t as the output
stream. See 输出流.