function getUsefulItems(usefulItems, item) {

    if (item.hasAttr('id') || item.isElem('style')) {

        usefulItems.push(item);
        item.parentNode = defs;

    } else if (!item.isEmpty()) {

        item.content.reduce(getUsefulItems, usefulItems);

    }

    return usefulItems;
}
Removes content of defs and properties that aren't rendered directly without ids.

@param {Object} item current iteration item
@return {Boolean} if false, item will be filtered out

@author Lev Solntsev