processStartTag method
Implementation
@override
Token processStartTag(StartTagToken token) {
  parser.parseError(
      token.span, 'expected-doctype-but-got-start-tag', {'name': token.name});
  anythingElse();
  return token;
}@override
Token processStartTag(StartTagToken token) {
  parser.parseError(
      token.span, 'expected-doctype-but-got-start-tag', {'name': token.name});
  anythingElse();
  return token;
}