link method
The definition for link label, matched case-insensitively and with
runs of whitespace collapsed, as CommonMark matches labels.
Implementation
MdLinkDefinition? link(String label) {
final lookups = _lookups;
if (lookups == null && _links.isEmpty) {
return null;
}
final key = normalizeLabel(label);
lookups?.add('l:$key');
return _links[key];
}