[Matthias247]

>> Minimum header overhead

> Wait, are you thinking about using UDP to transport HTTP?! Do you even know what your MTU is?

> If you're insane and send HTTP headers in each packet, you've wasted most of your data space.

I think header in the requirement just means protocol/PDU header, which is required to deploy any kind of higher level protocol on top of UDP. Just like the UDP header and the IP headers are used at the start of data received in ethernet frames. These headers can be anything depending on the use case, even only a single or even zero bytes. The whole document does not mention that sending HTTP headers on top of UDP (which obviously could cause MTU problems, but nevertheless this kind of mechanism was standardized with CoAP).