parseChildLines method
Implementation
List<Line?> parseChildLines(BlockParser parser) {
  // Grab all of the lines that form the block element.
  final childLines = <Line?>[];
  while (!parser.isDone) {
    final match = pattern.firstMatch(parser.current.content);
    if (match == null) break;
    childLines.add(parser.current);
    parser.advance();
  }
  return childLines;
}