Processors can be compared to "commands" or "actions". Prior to MODX 2.2, they were flat PHP files, but since then they have been based on the base
modProcessor class, and its various subtypes.
Useful reading around the web until this page is expanded:
- Getting started with class-based processors (at markhamstra.com)
- Extending modObjectGetListProcessor, a powerful class based processor in MODX 2.2 (at markhamstra.com)
- Full list of MODX Processors (at bobsguides.com)