anchor.diff:    ///
     /// Returns the nodes if it was successfully created, `null` otherwise.
     Iterable<Node>? _tryCreateReferenceLink(
  -    LinkContext context,
  +    _LinkContext context,
       String label,
     ) {
       final parser = context.parser;
  
positive.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)`.
  
negative.code:     String? tag,
      required List<Node> Function() 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 '('
  