I recently found an interesting 'language' from http://xplusplus.sourceforge.net/ - X Plus Plus - which is an object-oriented language that is entirely based on XML's syntactical structure. I had some thoughts about developing a language like this long back, but I felt that XML is not so powerful when it comes to expression handling and evaluation. Just think how much difficult it is, to represent an expression, purely in XML? I just had a quick look at X++. Have a look at it, and it may trigger some new concepts in you.