I get a segmentation fault when exit is put inside a function called from the start tag callback function :-

function exitFunction() {
  exit;
}

function startTagCallback($parser, $attributes) {
  if (!strCaseCmp($tag, "exit"))
    exitFunction();
}

If the function startTagCallback is setup as the start tag callback function then when exitFunction is called when an <EXIT> tag is found, the child process of the webserver will segmentation fault.