onMatch method
Processes match, adding nodes to parser and possibly advancing
parser.
Returns whether the caller should advance parser by match[0].length.
Implementation
@override
bool onMatch(InlineParser parser, Match match) {
var code = match[2]!.trim().replaceAll('\n', ' ');
if (parser._encodeHtml) code = escapeHtml(code);
parser.addNode(Element.text('code', code));
return true;
}