code: func (msg *MsgCFCheckpt) AddCFHeader(header *chainhash.Hash) error {
  	if len(msg.FilterHeaders) == cap(msg.FilterHeaders) {
  		str := fmt.Sprintf("FilterHeaders has insufficient capacity for "+
  			"additional header: len = %d", len(msg.FilterHeaders))
  		return messageError("MsgCFCheckpt.AddCFHeader", str)
  	}
  
  	msg.FilterHeaders = append(msg.FilterHeaders, header)
  	return nil
  }
docs: // AddCFHeader adds a new committed filter header to the message.