code: func (g *Graph) Parents(child *Key, orderBy string) ([]*Node, error) {
  	return g.orderedRelatives(child, "child", orderBy, (*Node).listParents)
  }
docs: // Parents returns direct parents of a node (given by its key).
  //
  // The order of the result depends on a value of 'orderBy':
  //   'key': nodes are ordered lexicographically by their keys (smaller first).
  //   'def': nodes are ordered by the order edges to them were defined during
  //        the execution (earlier first).
  //
  // Any other value of 'orderBy' causes an error.
  //
  // A missing node is considered to have no parents.
  //
  // Trying to use Parents before the graph has been finalized is an error.