The files which name ends in ".rules" will be read by udev in lexical order. Any others will be ignored. There are some example rules in rules.examples, take a look at those for an idea of what's possible with udev. When a rule matches in one file, a different rule in another file will be ignored, so be sure to name your own files properly. Be sure to leave rules files installed by the spell as they are, so the spell can update them when needed. If you need to make changes, always add your own rules files when possible.