function getArbitraryProperty(name, separator) {
  const arbitraryPropPattern = String.raw`^\[([a-z\-]*)${separator}\.*`;
  const arbitraryPropRegExp = new RegExp(arbitraryPropPattern);
  const results = arbitraryPropRegExp.exec(name);
  return results === null ? '' : results[1];
}
Returns the arbitrary property of className without the separator or an empty string if none
e.g. "[mask-type:luminance]" => "mask-type"

@see https://tailwindcss.com/docs/adding-custom-styles#arbitrary-properties
@param {String} name Classname suffix (without it variants) to be parsed
@param {String} separator The separator character as in config
@returns {String} The arbitrary property