Executable XML users challenge

provide any LISP macro with clear explanation of its structure and function
that is :
1.concise (max 10 lines)
2.does not have a C equivalent(at least not anything above 100 lines)
3.does not use any libraries or imported complex functions which are not in C
If you provide an exact explanation/commentary on what it does i'll try to make a C solution which
is equivalent to LISP one. If i fail to do so, LISP wins, if i provide a solution you can make another macro.
If all examples in the thread are provide with C equivalents, LISP loses.

>>200
You compaining the C lack the full string processing suite, which is a bunch of separate, external library.
You LISP compiler simply includes this string processing code built-in.
If i use a library(and i can choose any library regex/parser/interpreter, i'm not limited by Lisp) i could accomplish the same thing.
I could even embed a full-blown LISP intepreter library, but you could call this "cheating".