code: func (g *Graph) Bool(def ...bool) bool {
  	n, ok := _boolf(g.String())
  	if !ok {
  		if len(def) == 0 {
  			return false
  		}
  		return def[0]
  	}
  	return n
  }
docs: // Bool returns the node as a boolean. If the node is not a
  // boolean, it returns false, or the default value if given.