Wow! When reading the announcement Hub Firmware Beta 46.4 by @Cory_Heuschkel I followed the link to the http_button, just out of curiosity and noticed it utilised a library st.mdns!!!
I can’t find any documentation, but when I looked at the lua_libs-api_v3\st indeed there is an MDNS library. Excellent. (In fact it is also in v2)
I wish this had been documented as I spent many happy hours making another library work and I know @TAustin has also created an MDNS library