-a file name and a @acronym{MIME} type. If your Emacs supports drag
-and drop, you can also drop the file in the Message buffer.
+a file name and a @acronym{MIME} type.
+
+@vindex mml-dnd-protocol-alist
+@vindex mml-dnd-attach-options
+If your Emacs supports drag and drop, you can also drop the file in the
+Message buffer. The variable @code{mml-dnd-protocol-alist} specifies
+what kind of action is done when you drop a file into the Message
+buffer. The variable @code{mml-dnd-attach-options} controls which
+@acronym{MIME} options you want to specify when dropping a file. If it
+is a list, valid members are @code{type}, @code{description} and
+@code{disposition}. @code{disposition} implies @code{type}. If it is
+@code{nil}, don't ask for options. If it is @code{t}, ask the user
+whether or not to specify options.