code: func (g *Graph) Create(s string) *Graph {
  	n := g.Node(s)
  	if n == nil {
  		return g.Add(s)
  	}
  	n.Clear()
  	return n
  }
docs: // Create returns the first subnode whose string value is equal to the given string,
  // with its subnodes deleted. If not found, the node is created and returned.