unreadToValid method
Unwind to a valid node; this node is "valid" if its ancestry represents a complete symbol. If this node is not valid, put back the character and ask the parent to unwind.
scanner
scanner Returns symbol’s node
Implementation
SymbolNode unreadToValid(IScanner scanner) {
if (!_valid && _parent != null) {
scanner.unread();
return _parent!.unreadToValid(scanner);
}
return this;
}