Missing sufficient documentation Selection-Field-Type

[TheCadien]

The Selection-Field-Type Doc is missing Doc about the PHP Class and the Service Config / Service Tag.

Like :
https://github.com/sulu/sulu-workshop/blob/master/config/services.yaml#L44
and
https://github.com/sulu/sulu-workshop/blob/master/src/Content/EventSelectionContentType.php

[alexander-schranz]

I think its a little bit confusing but a Field-Type is not automatically a Content-Type. The docs is about the Admin UI and create new entities for it, for this no Content Type is needed.

Content Type are about pages and how a page should render it. Not sure so if admin-ui docs is the correct docs about Content-Type.

[alexander-schranz]

So I think this is related to #121

[TheCadien]

See your Point. What do you think, is the cookbook the better place:)?

[niklasnatter]

Unfortunately, the documentation about the field-types (and their difference to content-types) is basically not existent 😕 Because of this, its really hard to find a good place for documenting this.

In my opinion, the best solution at the moment would be adding an additional Register PHP content type paragraph/subsection to https://docs.sulu.io/en/latest/book/extend-admin.html#selection-field-type
This section should probably state that this is needed when the selection is used inside of a page and give a short example how to do it.