The listener is used by the Collection type as well as the Choice and Entity type (with multiple
selection). The effect is that you can have for example this model:
class Article
{
public function addTag($tag) { ... }
public function removeTag($tag) { ... }
public function getTags($tag) { ... }
}
You can create a form for the article with a field "tags" of either type "collection" or "choice"
(or "entity"). The field will correctly use the three methods of the model for displaying and
editing tags.
