This action is a GUI front-end to the core's <act>SaveTo</act> action. If you happen to pass a filename then <act>SaveTo</act> is called directly. Else, the user is prompted for a filename to save, and then <act>SaveTo</act> is called with that filename.

The DialogByPattern mode is intended for scripts and core: it presents a dialog box with format selection and listing patterns, but does not perform any real file operation just returns a filename*format string.