The package defines a single command \verbdef (which has a *-form, like \verb). \verbdef will define a robust command whose body expands to verbatim text. By using commands defined by \verbdef, one can put verbatim text into the arguments of commands; since the defined command is robust, it doesn't matter if the argument is moving. (Full details of syntax and caveats about use are in comments in the file itself.) The author is Robin Fairbairns.