In his new post on "Yet Another PHP Blog" (a blog documenting his participation in Google's Summer of Code), William Candillon talks about some issues he had when working on his aspect-oriented framework.
The original PHP compiler doesn't use AST representation of a source code so in the previous versions of phpAspect I had to fill the php grammar with my own AST constructions. It was a painful job and moreover I had to do it in each major version of PHP. For this new version, I'm using the yaxx project written by Dr. Yijun Yu. The yaxx tool is a yacc skeleton which build an xml ast representation of a source code according to his grammar.
He includes two images, one showing the simple class code and the other showing the tree that's obtained from the XML generated by the yaxx tool for that class structure.