get selectorStack() {
    var block
      , stack = [];
    for (var i = 0, len = this.stack.length; i < len; ++i) {
      block = this.stack[i].block;
      if (block.node && 'group' == block.node.nodeName) {
        block.node.nodes.forEach(function (selector) {
          if (!selector.val) selector.val = this.interpolate(selector);
        }, this);
        stack.push(block.node.nodes);
      }
    }
    return stack;
  }
Return the current selectors stack.

@return {Array}
@api private