code: func (bb *Builder) SetFileName(name string) *Builder {
  	baseName := filepath.Base(name)
  	if utf8.ValidString(baseName) {
  		bb.m["fileName"] = baseName
  	} else {
  		bb.m["fileNameBytes"] = mixedArrayFromString(baseName)
  	}
  	return bb
  }
docs: // SetFileName sets the fileName or fileNameBytes field.
  // The filename is truncated to just the base.