It works “fairly well” (in that it’s able to handle anything that the processing.org web site throws at it) but I’m sure its total scope is limited (until a proper parser is involved). I felt bad about tackling this using regular expressions until I found out that the original Processing code base did it in the same manner (they now use a real parser, naturally).
Another capability is to write code natively in the Processing language. This allows you to make use of extended language features such as method overloading and classic inheritance, though it looks like type information is pretty much ignored.
John has many of the demos from processing.org working. Most of them are going to peg your CPU, but this is some seriously cool stuff to see working in a first release.