code: func MustRender(c context.Context, out io.Writer, name string, args Args) {
  	if b, _ := c.Value(&contextKey).(*boundBundle); b != nil {
  		b.MustRender(c, b.Extra, out, name, args)
  		return
  	}
  	panic(errNoBundle)
  }
docs: // MustRender renders the template into the output writer or panics.
  //
  // It never writes partial output. It also panics if attempt to write to
  // the output fails.