i assumed webusb was entirely host-side, but apparently a device can provide a descriptor specifying a URI to the intended compatible page, and that seems to be one of the features of this PR.
the 0x22 request type isn't part of any webusb standard, it is from a tinyusb example program where they demo connecting webusb and webserial to the same device, which is a little strange and probably not what you're doing with the rp2040.
https://developer.chrome.com/articles/build-for-webusb/#webu...
the rest of it seems a little strange. the webserial API should be able to talk to any class-compliant serial device, that's already supported.
https://developer.chrome.com/articles/serial/#open-port
the 0x22 request type isn't part of any webusb standard, it is from a tinyusb example program where they demo connecting webusb and webserial to the same device, which is a little strange and probably not what you're doing with the rp2040.