describe-mode function provides information about major modes. It is normally bound to
C-h m. It uses the value of the variable
major-mode (see Major Modes), which is why every major mode command needs to set that variable.
command describe-mode \&optional buffer
This command displays the documentation of the current buffer’s major mode and minor modes. It uses the
documentation function to retrieve the documentation strings of the major and minor mode commands (see Accessing Documentation).
If called from Lisp with a non-
buffer argument, this function displays the documentation for that buffer’s major and minor modes, rather than those of the current buffer.