message: Transform only valid id attributes
diff: @@ -235,6 +235,12 @@ export const plugin: Plugin = {
  let val = token.val;
  val = val.substring(1, val.length - 1);
  val = val.trim();
  + const validIdNameRegex: RegExp = /^-?[_a-zA-Z]+[_a-zA-Z0-9-]*$/;
  + if (!validIdNameRegex.test(val)) {
  + val = makeString(val, singleQuote ? "'" : '"', false);
  + result += `id=${val}`;
  + break;
  + }
  // Write css-id in front of css-classes
  const position: number = startTagPosition;
  result = [result.slice(0, position), `#${val}`, result.slice(position)].join(
  