Using Preferred Applications from the CLI

I can use a command-line interface to invoke (not just "set," but "invoke") my GUI preferences.

System-> Preferences -> Preferred Applications lets me set things like my preferred email application and preferred browser. Works fine in the GUI, but how about from the command line?

The solution is XDG tools, from the Portland Project. Browse a url or edit a file?

xdg-open https://google.com
xdg-open /tmp/foo.txt

Email?

xdg-email