code: func (b *Bundle) RegisterUnmarshalFunc(format string, unmarshalFunc UnmarshalFunc) {
  	if b.unmarshalFuncs == nil {
  		b.unmarshalFuncs = make(map[string]UnmarshalFunc)
  	}
  	b.unmarshalFuncs[format] = unmarshalFunc
  }
docs: // RegisterUnmarshalFunc registers an UnmarshalFunc for format.