When I’m coding a new ESP-HomeKit accessory I use the free HomeKit Accessory Protocol Specification (Non-Commercial Version) form Apple. To see how to use the characteristics and what type of options there are for a specific type of accessory. All you need or want to know can be found in this protocol.
HomeKit Accessory Protocol (HAP) is Apple’s proprietary protocol that enables third-party accessories in the home (e.g., lights, thermostats and door locks) and Apple products to communicate with each other. HAP supports two transports, IP and Bluetooth LE. The information provided in the HomeKit Accessory Protocol Specification (Non-Commercial Version) describes how to implement HAP in an accessory that you create for non-commercial use and that will not be distributed or sold.
How do I access the specification?
The HomeKit Accessory Protocol Specification (Non-Commercial Version) can be downloaded from the HomeKit Apple Developer page. Before downloading the file, you will need to sign in with your Apple ID, then review and execute a click-through agreement.
How will a commercial HomeKit accessory be different from an accessory that I create using this specification?
Unlike a non-commercial HomeKit accessory, a HomeKit accessory that will be distributed or sold must incorporate the Apple Authentication Coprocessor, obtain Wi-Fi Alliance certification or Bluetooth SIG certification depending on the transport used, and complete HomeKit certification under the MFi Program. At a user level, a non-commercial accessory will use a different process for on-boarding an IP-based accessory to the network, and will present a warning dialog in iOS that the user must acknowledge before continuing.
Where can I ask more questions about implementing HAP?
To ask technical questions and discuss the HomeKit Accessory Protocol with other developers and smart home enthusiasts, visit the Apple Developer Forums.
Note: To produce and sell HomeKit compatible accessories, your company need to be certified for that (https://developer.apple.com/homekit/, If you’re interested in developing or manufacturing a HomeKit accessory that will be distributed or sold, your company must enroll in the MFi Program.) Espressif have their implementation of HomeKit framework, but it will give you it only if you have MFi certification (notice this text at the bottom of page you mentioned: Please note that the Espressif HomeKit SDK is available to MFi licensees only, and you need to provide the Account Number for verification purposes when requesting the SDK.).This project is a non-commercial implementation of HAP protocol, not meant for commercial use.