PHP has a default limit of 100 before it dies:
Fatal error: Maximum function nesting level of '100' reached, aborting!
Edit: You can change the limit with ini_set('xdebug.max_nesting_level', 100000);
, but if you go above about 1150 iterations PHP crashes:
[Fri Oct 24 11:39:41 2008] [notice] Parent: child process exited with status 3221225477 -- Restarting.