code: func serviceTagFilter(sn *structs.ServiceNode, tag string) bool {
  	tag = strings.ToLower(tag)
  
  	// Look for the lower cased version of the tag.
  	for _, t := range sn.ServiceTags {
  		if strings.ToLower(t) == tag {
  			return false
  		}
  	}
  
  	// If we didn't hit the tag above then we should filter.
  	return true
  }
docs: // serviceTagFilter returns true (should filter) if the given service node
  // doesn't contain the given tag.