maximum z-index on the page

gistfile1.js

var highest_index = 0, 
    elements = document.getElementsByTagName('*');
for (var i = 0; i < elements.length - 1; i++) {
    if (parseInt(elements[i].style.zIndex) > highest_index) {
        highest_index = parseInt(elements[i].style.zIndex);
    };
};
var zIndex = highest_index + 10;