Formally, they're absolutely right. Information like that is out of band with HAL.
In practice, I deal with it by sticking to HTTP verb conventions and specifying what to do in the documentation.
It's not automatic -- it'd be e.g. rsrc.somelink.post(params) instead of rsrc.somelink(params) in HyperResource's case -- but it works, and any human who knows what the 'somelink' rel is supposed to do might also be expected to know how to use it.
In practice, I deal with it by sticking to HTTP verb conventions and specifying what to do in the documentation.
It's not automatic -- it'd be e.g. rsrc.somelink.post(params) instead of rsrc.somelink(params) in HyperResource's case -- but it works, and any human who knows what the 'somelink' rel is supposed to do might also be expected to know how to use it.