@samdark I'm sorry to have caused confusion.

> It doesn't have anything to do with chaining. Chaining is just request methods returning the instance of request that collects data including headers.

Right, this specific conversation has nothing to do with chaining. I was suggesting that should go into @mtdowling's PR, which is a fork of this. 

> Type hinting doesn't make sense for an object that accepts any key-value pairs. It is a wrapper for the purpose of having a wrapper.

Instead of a method expecting `array` it can type hint against `HeaderValuesInterface`, which is marginally more useful in some scenarios. I wasn't trying to suggest that we need type hinting on the key/value pair strings or anything weird like that.