code: function buildGraph(graph, defs, child, index) {
      var i = defs.length - 1;
      if (i < 0) return [];
  
      // tail
      if (i) child = new Node(graph, createTransformDef(defs[i]), child, index);
      while (--i > 0) child = new Node(graph, createTransformDef(defs[i]), child, 0);
  
      return buildGraphHead(graph, defs[0], child);
    }
docs: graph building