The project #micro HTTP server in C is designed to implement this protocol. This is where you'll find the low-level details discussions.
This project documents the protocol itself, its definitions and evolutions, to help other clients and server interoperate.
HTTaP could be described as an attempt to formalise requests and replies between a HTTP-capable client and server, as well as all the surrounding parameters.
Think of HTTaP as a WebAPI for hardware and logic circuits.
For example it can embed/encapsulate SCPI commands over Ethernet or Wifi instead of RS232 or USB. No need to install stupid Windows drivers or lousy (binary, non-free and obfuscated) applications !
HTTaP messages are very simple : just "get" or "put" values at certain places, using JSON notation. Simple but limited so actual work is achieved through convoluted sequences of small atomic messages.
Standard addresses provide well-known points that provide enough informations to discover/explore the system, its hierarchy and capabilities, through individual client requests.
The user is normally directly connected to the server so the latency is usually low and HTTaP doesn't implement elaborate bandwidth-enhancement algorithms. Real-time latency matters more because it is usually connected to a GUI.