Editres is a pretty powerful program for displaying and even modifying properties of widgets within an application window. I believe it interfaces with the X resources. However, very few programs actually understand its protocol (for instance, Firefox does not). Is there a similar program or perhaps a command line tool for displaying widget hierarchy in any given window? A program like xprop will work on any window in the X Window System, but it (as far as I know) only retrieves information about an entire window and not the widget tree within it.
For context, I am working with the GNOME desktop environment on Red Hat Enterprise Linux.
Many modern widget toolkits don’t use X windows for each widget, but instead manage the widgets manually as part of the library. As such, there’s no protocol to intercept like you can with traditional X programs. These toolkits do expose widget tree information in other ways, though. GTK 2 had https://live.gnome.org/Accerciser, which appears to work with GTK 3.