Enable web applications to register themselves as handlers of custom URL protocols/schemes using their installation manifest.
Native applications often register themselves as protocol handlers to increase discoverability and usage. While websites currently have this ability to register to handle schemes via registerProtocolHandler(), it is desirable to have web apps be first-class citizens and be launched directly when a custom-scheme link is invoked.
Docs: https://docs.google.com/document/d/1NHlWLjAPZ-dyxcz3AoTWibeerDeHW7Vqrx6FmhB0XmE
Samples: https://protocol-handler.glitch.me/ https://fabiorocha.github.io/pwa
Explainers: https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/master/URLProtocolHandler/explainer.md https://web.dev/url-protocol-handler/