Populating a dropdown with values from a (sub-) category
Using DPL query
(Solution found at: https://www.mediawiki.org/wiki/Extension_talk:DynamicPageList3#Return_page_titles_as_plain_text?
| {{{field
| dokumententyp
| input type=dropdown
| values = {{#dpl: namespace = Category
| category = Dokumententyp
| mode = inline
| format = ,¶%TITLE%,,
| inlinetext = ,
}}
}}}