code: func (p *Pusher) Format(format expfmt.Format) *Pusher {
  	p.expfmt = format
  	return p
  }
docs: // Format configures the Pusher to use an encoding format given by the
  // provided expfmt.Format. The default format is expfmt.FmtProtoDelim and
  // should be used with the standard Prometheus Pushgateway. Custom
  // implementations may require different formats. For convenience, this
  // method returns a pointer to the Pusher itself.