Hi Klaus,
concerning "It doesn't help that there is no SAP documentation for available annotations...".
That is not completely true although there is no central landing page to identify them all, but the ABAP keyword help on ABAP CDS views contains a description of the available annotations at the relevant keywords. Currently, that is for view definition and elements in a select list:
As Thomas already stated the annotation your are looking for is not available in NW 7.40. It should come with NW 7.50 with a lot of other annotations that will make life easier (especially when thinking about UI integration). This is also the reason you should use the semantic annotations available at the moment although they are not really of use in the current NW release
Best regards
Christian