code: func (g *BuilderGroup) Groups() []*BuilderGroup {
  	groups := []*BuilderGroup{}
  	for child, parent := range g.builder.ring.GroupToGroup {
  		if parent == g.index {
  			groups = append(groups, g.builder.groups[child])
  		}
  	}
  	return groups
  }
docs: // Groups returns the slice of groups that are the direct children of this
  // group.