code: func Compare(a, b Labels) int {
  	l := len(a)
  	if len(b) < l {
  		l = len(b)
  	}
  
  	for i := 0; i < l; i++ {
  		if d := strings.Compare(a[i].Name, b[i].Name); d != 0 {
  			return d
  		}
  		if d := strings.Compare(a[i].Value, b[i].Value); d != 0 {
  			return d
  		}
  	}
  	// If all labels so far were in common, the set with fewer labels comes first.
  	return len(a) - len(b)
  }
docs: // Compare compares the two label sets.
  // The result will be 0 if a==b, <0 if a < b, and >0 if a > b.