parse method
Implementation
@override
Node? parse(BlockParser parser) {
final lines = <Line>[parser.current];
parser.advance();
while (!BlockSyntax.isAtBlockEnd(parser)) {
lines.add(parser.current);
parser.advance();
}
if (!_parseLinkReferenceDefinition(lines, parser)) {
parser.retreatBy(lines.length);
}
return null;
}