The documentation still lack information how to set up the transform

[kanitw]

The docs jumps into the documentation for syntax right away.

There should be a paragraph explaining the key concepts and key properties of the transform first. (See transform docs such as https://vega.github.io/vega/docs/transforms/stack/)

Given the current state of the docs, new users might not know that there is a concept of base mark, which is basically based on reactive geometry (and may get confused what is a base mark when they see the parameter avoidBaseMark).