LEVEL should be either :debug, :warning, :error, or :emergency
\(but see `warning-minimum-level' and `warning-minimum-log-level').
+Default is :warning.
:emergency -- a problem that will seriously impair Emacs operation soon
if you do not attend to it promptly.
Aside from generating the message with `format',
this is equivalent to `display-warning'.
-TYPE is the warning type: either a custom group name (a symbol).
+TYPE is the warning type: either a custom group name (a symbol),
or a list of symbols whose first element is a custom group name.
\(The rest of the symbols represent subcategories and
can be whatever you like.)