parameter implementation-detail doesn't seem to work

[akrzemi1]

I have a nested "detail" namespace ak_toolkit::markable_ns::detail_.
I have tried putting the following lines into my mrdocs.yml file:

implementation-detail: 'detail_'

implementation-detail: detail_

implementation-detail: 'ak_toolkit::markable_ns::detail_'

implementation-detail: ak_toolkit::markable_ns::detail_

But in any case, declarations from namespace ak_toolkit::markable_ns::detail_ still show up in the generated docs.