7 classes are annotated with BetterExposedFiltersFilterWidget in Better Exposed Filters 8.4

DatePickers in src/Plugin/better_exposed_filters/filter/DatePickers.php

JQuery UI date picker widget implementation.

DefaultWidget in src/Plugin/better_exposed_filters/filter/DefaultWidget.php

Default widget implementation.

Hidden in src/Plugin/better_exposed_filters/filter/Hidden.php

Default widget implementation.

Links in src/Plugin/better_exposed_filters/filter/Links.php

Default widget implementation.

RadioButtons in src/Plugin/better_exposed_filters/filter/RadioButtons.php

Default widget implementation.

Single in src/Plugin/better_exposed_filters/filter/Single.php

Single on/off widget implementation.

Sliders in src/Plugin/better_exposed_filters/filter/Sliders.php

JQuery UI slider widget implementation.