I have a few questions regarding Transmit Security WebauthN SDK: cross devices flow, user reg from a device and device support for WebauthN

Question

For Cross Device flow - Why are event handlers needed, and what is the lifecycle? How do I know if a user has already registered on a particular device? How do I know if a device support WebAuthn? What do I do if it is not supported?

Any support or advice appreciated for above questions