code: func (b *Builder) Labels() Labels {
  	if len(b.del) == 0 && len(b.add) == 0 {
  		return b.base
  	}
  
  	// In the general case, labels are removed, modified or moved
  	// rather than added.
  	res := make(Labels, 0, len(b.base))
  Outer:
  	for _, l := range b.base {
  		for _, n := range b.del {
  			if l.Name == n {
  				continue Outer
  			}
  		}
  		for _, la := range b.add {
  			if l.Name == la.Name {
  				continue Outer
  			}
  		}
  		res = append(res, l)
  	}
  	res = append(res, b.add...)
  	sort.Sort(res)
  
  	return res
  }
docs: // Labels returns the labels from the builder. If no modifications
  // were made, the original labels are returned.