code: func NewMulti(vals ...interface{}) LogBackend {
  	if len(vals)%2 != 0 {
  		Fail(e.New("parameters must be in pair of LogBackend and Formatter"))
  		return nil
  	}
  	l := len(vals) / 2
  	mp := make([]LogBackend, 0, l)
  	for i := 0; i < len(vals); i += 2 {
  		bak, ok := vals[i].(LogBackend)
  		if !ok {
  			Fail(e.New("not a LogBackend"))
  			return nil
  		}
  		f, ok := vals[i+1].(Formatter)
  		if !ok {
  			Fail(e.New("not a Formatter"))
  			return nil
  		}
  		bak.F(f)
  		mp = append(mp, bak)
  	}
  	return &MultiLog{
  		mp: mp,
  	}
  }
docs: //NewMulti creates a MultiLog