How can you figure out the highest z-index in your document?

Stealing some code from abcoder site for the sake of clarity:

  var maxZ = Math.max.apply(null, 
    $.map($('body *'), function(e,n) {
      if ($(e).css('position') != 'static')
        return parseInt($(e).css('z-index')) || 1;
  }));