How to Create Custom Content Type Plugin for MT

Hi, I'm new to MT, but have developed with other CMSs. I'm looking for a small bit of information to get started. I'm wondering if MT has a generic content class and table that custom content types can be built off of -- like nodes in Drupal or such. I'm also hoping to do as much of my development in PHP. I've found the plugin docs, which don't come at things from quite the angle I am describing - so I wonder if perhaps there is an existing plugin that creates a custom content type that I could look at, and mimick, and wonder if there is any documentation about how do to this all in PHP, or how much can be done in PHP.

Thank you in advance.
W