Bug#869386: on man page say what ! means

[積丹尼 Dan Jacobson]

Package: libgtk-3-bin
Version: 3.22.16-1
Severity: wishlist
File: /usr/share/man/man1/gtk-query-settings.1.gz

$ gtk-query-settings  theme
                     gtk-theme-name: "HighContrast"
                gtk-icon-theme-name: "HighContrast"
!           gtk-fallback-icon-theme: NULL
                 gtk-key-theme-name: NULL
              gtk-cursor-theme-name: NULL
              gtk-cursor-theme-size: 0
               gtk-sound-theme-name: "freedesktop"
  gtk-application-prefer-dark-theme: FALSE

The man page should say what ! means.

Also it should say if it is querying gtk 2 or 3 or both settings.