What happened to fill-slot="content"

Earlier, it was possible to use fill-slot="content' , 'content-core' an 'main'.

It looks like only main and content-core are left in Plone 5.2.

If I remember right: fill-slot="content" did not 'remove' IAboveContentTitle (fill-slot="main" does)

No change that I can see...

If i put

  <metal:block fill-slot="main">xxx</metal:block>

In my view.pt, it works ( I see xxx ). Same with fill-slot="content-core"

But if I change it to

  <metal:block fill-slot="content">xxxx</meatal:block>

I get nothing…

Maybe it is a diazo rule in the newest barceloneta or something (?)