mixin(nodes, block) {
    if (!nodes.length) return;
    var len = block.nodes.length
      , head = block.nodes.slice(0, block.index)
      , tail = block.nodes.slice(block.index + 1, len);
    this._mixin(nodes, head, block);
    block.index = 0;
    block.nodes = head.concat(tail);
  }
Mixin the given `nodes` to the given `block`.

@param {Array} nodes
@param {Block} block
@api private