code: func MatchFilterHandler(key string, value interface{}, h Handler) Handler {
  	return FilterHandler(func(r *Record) (pass bool) {
  		switch key {
  		case r.KeyNames.Lvl:
  			return r.Lvl == value
  		case r.KeyNames.Time:
  			return r.Time == value
  		case r.KeyNames.Msg:
  			return r.Msg == value
  		}
  
  		for i := 0; i < len(r.Ctx); i += 2 {
  			if r.Ctx[i] == key {
  				return r.Ctx[i+1] == value
  			}
  		}
  		return false
  	}, h)
  }
docs: // MatchFilterHandler returns a Handler that only writes records
  // to the wrapped Handler if the given key in the logged
  // context matches the value. For example, to only log records
  // from your ui package:
  //
  //    log.MatchFilterHandler("pkg", "app/ui", log.StdoutHandler)
  //