API documentation about Liquid::Tag

Where can we get detailled information on Liquid internal API? That would be very useful for writing Liquid plugins (right now I’m trying with a Tag plugin).

The problem is that nothings seems to be documented. The rubydoc is really poor: RubyDoc.info: Class: Liquid::Tag – Documentation for liquid (5.11.0) – RubyDoc.info

Especially, what is the tokens argument passed to the Tag constructor? How to use it?