selectedValues() {
        throw new Error("ClassificationBase mixin model needs to implement selectedValues method in views");
      }
This is a mixin for a control-tag that is a base of creating classification-like tags.
A classification tag is a tag that can be applied to the object tag and does not create a region related to the object-tag nature
@see PerRegionMixin which allows to apply a created result to a region related to an object-tag nature
@see PerItemMixin which allows to apply a created result to just one object-item provide by object-tag (@see MultiItemsMixin)