D. X Options and Resources

You can customize some X-related aspects of Emacs behavior using X resources, as is usual for programs that use X. On MS-Windows, you can customize some of the same aspects using the system registry. See section The MS-Windows System Registry. Likewise, Emacs on MacOS Carbon emulates X resources using the Preferences system. See section Environment Variables and Command Line Arguments..

When Emacs is built using an “X toolkit”, such as Lucid or LessTif, you need to use X resources to customize the appearance of the widgets, including the menu-bar, scroll-bar, and dialog boxes. This is because the libraries that implement these don't provide for customization through Emacs. GTK+ widgets use a separate system of “GTK resources”, which we will also describe.