xdg-settings man page: document how to show all it knows
On the xdg-settings man page, perhaps mention how to dump all that it knows:
$ xdg-settings --list|perl -wnle 'print $1 if /^\s+(\S+)/'|xargs -n 1 --verbose xdg-settings get
xdg-settings get default-url-scheme-handler
xdg-settings get default-web-browser
google-chrome-unstable.desktop