Siri has recently had a big Human Interface Guidelines update, notably the Apple Health, Apple Pay and Sign in, and new content as well.
Editorial Guidelines, Shortcuts & Suggestions, Custom Intents and System Intents have all received new content. Developers who are working on creating apps with Siri capability and functionality should read up on the new features and see how it could be implemented.
Developers mainly utilize SiriKit for adding Siri functionality to their accessory or app. Apple’s Human Interface Guidelines act as a cheat sheet on how they could implement the new content in the best way possible- for instance, allowing another person’s iPhone play music via AirPlay 2, switching the smart light on using HomeKit and having Siri order a coffee for you.
The Human Interface Guidelines documentation is available for anyone who want to know more- visit the official Apple developer website and look for the Human Interface Guidelines section.