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Translations:Xorg/Guide/53/en
From Gentoo Wiki (test)
Most of the configuration files for Xorg are stored in /etc/X11/xorg.conf.d/. Each file is given a unique name and ends in .conf. The file names in Xorg's configuration directory will be read in alpha numeric order. For example, 10-evdev.conf will be read before 20-synaptics.conf; a-evdev.conf will be read before b-synaptics.conf, and so on. The files in this directory are not required to be numbered, but doing so will help to keep them organized. Organization is helpful when debugging faulty configuration files.