Developing Movable Type Plug-ins: The ease of developing plugins for Movable Type — and their consequent ubiquity — is one of the things that’s made it so popular. If it doesn’t exist, someone will invent it.
“Movable Type provides developers with a framework to easily and elegantly extend the base functionality of the system using OO Perl. Generally speaking, plugins are limited to MT’s template processing engine, to add variable, container, and conditional tags in addition to global filters. In version 2.6, the plugin framework began to branch out from template processing by introducing an API for hooking in text-formatting engines and access to MT’s data persistence mechanisms.”