tag function
Implementation
Parser tag() => (tagStart() &
ref0(identifier).trim() &
ref0(tagContent).optional().trim() &
ref0(filter).star().trim() &
tagEnd())
.map((values) {
final name = (values[1] as Identifier).name;
final content = collapseTextNodes(values[2] as List<ASTNode>? ?? []);
final filters = (values[3] as List).cast<Filter>();
final nonFilterContent =
content.where((node) => node is! Filter).toList();
return Tag(name, nonFilterContent, filters: filters);
}).labeled('tag');