anchor.diff:      String? tag,
       required List<Node> Function() getChildren,
     }) {
  -    final context = LinkContext(parser, opener, getChildren);
  +    final context = _LinkContext(parser, opener, getChildren);
       final text = parser.source.substring(opener.endPos, parser.pos);
       // The current character is the `]` that closed the link text. Examine the
       // next character, to determine what type of link we might have (a '('
  
positive.code:   ///
    /// Returns the nodes if it was successfully created, `null` otherwise.
    Iterable<Node>? _tryCreateReferenceLink(
      LinkContext context,
      String label,
    ) {
      final parser = context.parser;
  
negative.code: 
  /// A helper class holds params of link context.
  /// Footnote creation needs other info in [_tryCreateReferenceLink].
  class _LinkContext {
    final InlineParser parser;
    final SimpleDelimiter opener;
    final List<Node> Function() getChildren;
  
    const _LinkContext(this.parser, this.opener, this.getChildren);
  }
  
  /// Matches links like `[blah][label]` and `[blah](url)`.
  