Under the "features" and "default-features" headline, the manifest documentation for users states:

There's also the "supports" field, which again acts exactly like the "supports" field on the global package.

https://github.com/microsoft/vcpkg/blame/master/docs/users/manifests.md#L228-L229

However, there is no such field in the schema:

And the vcpkg tool complains if you try to use it (here the attempt to use it for a new feature in a port, not in manifest mode):

$ ./vcpkg format-manifest ports/libmicrohttpd/vcpkg.json 
Failed to parse manifest file: /vcpkg/ports/libmicrohttpd/vcpkg.json
Errors occurred while parsing /vcpkg/ports/libmicrohttpd/vcpkg.json
    $.features.https (a feature): unexpected field 'supports', did you mean 'description'?

So what is the state of the supports field in dependenciesfeatures?