public static function getId($id) {
    $id = str_replace([' ', '_', '[', ']'], ['-', '-', '-', ''], Unicode::strtolower($id));

    // As defined in http://www.w3.org/TR/html4/types.html#type-name, HTML IDs can
    // only contain letters, digits ([0-9]), hyphens ("-"), underscores ("_"),
    // colons (":"), and periods ("."). We strip out any character not in that
    // list. Note that the CSS spec doesn't allow colons or periods in identifiers
    // (http://www.w3.org/TR/CSS21/syndata.html#characters), so we strip those two
    // characters as well.
    $id = preg_replace('/[^A-Za-z0-9\-_]/', '', $id);

    // Removing multiple consecutive hyphens.
    $id = preg_replace('/\-+/', '-', $id);
    return $id;
  }