code: func (f *file) containsComments(start, end token.Pos) bool {
  	for _, cgroup := range f.f.Comments {
  		comments := cgroup.List
  		if comments[0].Slash >= end {
  			// All comments starting with this group are after end pos.
  			return false
  		}
  		if comments[len(comments)-1].Slash < start {
  			// Comments group ends before start pos.
  			continue
  		}
  		for _, c := range comments {
  			if start <= c.Slash && c.Slash < end && !strings.HasPrefix(c.Text, "// MATCH ") {
  				return true
  			}
  		}
  	}
  	return false
  }
docs: // containsComments returns whether the interval [start, end) contains any
  // comments without "// MATCH " prefix.