* Default case (when none of the rules matched) is handled properly with ``*`` rule (line 16).
**Never forget to handle default case, otherwise control flow in lexer will be undefined for some input strings.**
- Use `[-Wundefined-control-flow] <../manual/warnings/wundefined_control_flow.html>`_ re2c warning:
+ Use `[-Wundefined-control-flow] <../manual/warnings/undefined_control_flow/wundefined_control_flow.html>`_ re2c warning:
it will warn you about unhandled default case and show input patterns that are not covered by the rules.
* We use the *sentinel* method to stop at the end of input (``re2c:yyfill:enable = 0;`` at line 8).