code: function renderStatic (
    index,
    isInFor
  ) {
    var cached = this._staticTrees || (this._staticTrees = []);
    var tree = cached[index];
    // if has already-rendered static tree and not inside v-for,
    // we can reuse the same tree.
    if (tree && !isInFor) {
      return tree
    }
    // otherwise, render a fresh tree.
    tree = cached[index] = this.$options.staticRenderFns[index].call(
      this._renderProxy,
      null,
      this // for render fns generated for functional component templates
    );
    markStatic(tree, ("__static__" + index), false);
    return tree
  }
docs: /* 
  Runtime helper for rendering static trees.