code: function add(element, stickyClone) {
        stickyClone.addClass('md-sticky-clone');
  
        var item = {
          element: element,
          clone: stickyClone
        };
        self.items.push(item);
  
        $mdUtil.nextTick(function() {
          contentEl.prepend(item.clone);
        });
  
        debouncedRefreshElements();
  
        return function remove() {
          self.items.forEach(function(item, index) {
            if (item.element[0] === element[0]) {
              self.items.splice(index, 1);
              item.clone.remove();
            }
          });
          debouncedRefreshElements();
        };
      }
docs: *************
  Public
  ************* Add an element and its sticky clone to this content's sticky collection