This month I have added support for custom ModelDoc nodes. These are general purpose nodes that can carry data on each model, which is then accessible from code. They work similarly to custom entities in Hammer, you define a struct or a class in C#:
attribute 'class' not allowedattribute 'contenteditable' not allowedattribute 'blocktype' not allowedattribute 'data-image-style' not allowed
The node then can be applied in ModelDoc, and accessed in an entity like so:
attribute 'class' not allowedattribute 'contenteditable' not allowedattribute 'blocktype' not allowedattribute 'data-image-style' not allowed
I have also added support of a variation of the these nodes called model break commands, they work similarly but have a callback for when the model breaks into its break pieces. The base addon has a bunch of examples for both types of these custom nodes.