Note: for Do it, Senders of it, etc., a null selection will be expanded to a word or to the current line in an attempt to do what you want.  Also note that Senders/Implementors of it will find the outermost keyword selector in a large selection, as when you have selected a bracketed expression or an entire line.  Finally note that the same cmd-m and cmd-n (and cmd-v for versions) work in the message pane of most browsers.
Enclose the selection in a kind of bracket.  Each is a toggle.
Ctrl-""	Enclose within "" and "", or remove enclosing "" and ""