ActionScript 3.0 was a great example of implementing E4X.

I miss that language a lot. It has quite a few great concepts: XML, intuitive implementation of objects, where key can be anything. Statically typed. Prototypes. Typed vectors. for..each loop. Dictionary with weak keys (oh that I loved so much, it was so powerful to implement better memory management on top of this).

I spent like 10 years developing in it, now it's my 6 year since I've touched it last time : (