When searching for features on the map, it's useful to have auto-complete or type-ahead functionality to prompt users with valid values.
It is possible to use GeoServer as the source for the typeahead with a few modifications to the standard TypeAhead code.
See the demo at https://slead.github.io/GeoServer_TypeAhead/ which also shows how Leaflet.js and Tokenfield can be integrated.
The source code is available at https://github.com/slead/GeoServer_TypeAhead