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) {
if (substitute == null) {
// Just use the original matched text.
parser.advanceBy(match[0]!.length);
return false;
}
// Insert the substitution.
parser.addNode(Text(substitute!));
return true;
}