I only followed your recommandation ;) From [5. Edit the content of an existing game](https://github.com/dartlangfr/game-store-codelab/blob/master/user-story-5.md) :

> - To create a two-way filter, implement a `Transformer` class (No docs :( see [Bind number to text field with filter  example](https://github.com/sethladd/dart-polymer-dart-examples/tree/master/web/bind_number_to_text_field_with_filter))

This brings me to https://github.com/sethladd/dart-polymer-dart-examples-unmaintained/blob/master/web/bind_number_to_text_field_with_filter/ui_filters.dart and _Copy_/_Paste_ made the rest :)