"We could do the same with XML. Of course the line above isn't really a list, it's a tree, just like its XML-alternative. Don't let references to lists confuse you, it's just that lists that contain other lists and trees are effectively the same thing. Lisp may stand for List Processing, but it's really tree processing - no different than processing XML nodes." (defmacro)

If you have a spare 20 minutes, read this excellent introduction to LISP.

"Everything we've learned about Lisp so far can be summarized by a single statement: Lisp is executable XML with a friendlier syntax. "