/**
 * The document observer handler.
 *
 * @param {Array} mutations The mutations to handle.
 *
 * @returns {undefined}
 */
function documentObserverHandler(mutations) {
   var mutationsLen = mutations.length;

   for (var a = 0; a < mutationsLen; a++) {
      var mutation = mutations[a];
      var addedNodes = mutation.addedNodes;
      var removedNodes = mutation.removedNodes;

      // Since siblings are batched together, we check the first node's parent
      // node to see if it is ignored. If it is then we don't process any added
      // nodes. This prevents having to check every node.
      if (addedNodes && addedNodes.length && !getClosestIgnoredElement(addedNodes[0].parentNode)) {
         initElements(addedNodes);
      }

      // We can't check batched nodes here because they won't have a parent node.
      if (removedNodes && removedNodes.length) {
         removeElements(removedNodes);
      }
   }
}