Draft: DO NOT MERGE! CSS clip/mask investigation
This branch is created to create some notes about the refactoring that will be needed to fix the issue. The main goal is to change the way clips and masks are loaded so that they act like any other css property and are not forced to be attributes.
There is a LOT that will go wrong when this change is done, so it should not be contemplated until after 1.2
Fixes #2652