code: func (p *tagDiffProcessor) diff(a, b []string) []string {
  	var found bool
  	c := make([]string, 0)
  	for _, v1 := range a {
  		for _, v2 := range b {
  			if v1 == v2 {
  				found = true
  			}
  		}
  		if !found {
  			c = append(c, v1)
  		}
  		found = false
  	}
  	return c
  }
docs: // diff is what diffOldNew and diffNewOld hand off to.