function createMarkupForCustomAttribute(
  name: string,
  value: mixed,
): string {
  if (!isAttributeNameSafe(name) || value == null) {
    return '';
  }
  return name + '=' + quoteAttributeValueForBrowser(value);
}
Creates markup for a custom property.

@param {string} name
@param {*} value
@return {string} Markup string, or empty string if the property was invalid.