LwIP mDNS SUBTYPES

Hello eveyrone,
I'm using the mDNS protocol implementation on lWIP, I need to use subtype for an mDNS service but there is not any function or macro that could be used to set the subtype of a service. (thing existes in the standards and many other mDNS implementations on linux), Does anyone have an idea or the same issue before ?
thanks in advance

The issue requests mDNS service subtype support in the lwIP implementation but names no file, entry point, or test. Start by locating the mDNS service-registration API and comparing it with the mDNS standard; done means the implementation provides a way to register a service subtype and verifies the resulting advertisement.

Written by the indexing model from the issue text.