What happened to that great ASTMatcher/Tooling doc?

Hi Sam, I remember a while back you posted some fantastic
documentation about tooling/astmatchers (it was a google doc IIRC).
What ever happened to that? I would really like to see that material
pulled into docs/ or at least being linked to.

-- Sean Silva

I think, this was the link: https://docs.google.com/document/d/1oTkVLhCdRJUEH1_LDaQdXqe8-aOqT5GLDL9e4MhoFF8/edit