Determining the primary pointer - note about mice?

[patrickhlauke]

Currently https://w3c.github.io/pointerevents/#determining-the-primary-pointer makes an implicit assumption that there will never be more than one concurrent mouse input

a pointer is considered primary if: [...] The pointer represents a mouse device.

This of course reflects the current reality where no OS allows for 2 or more mice to be active (in most cases, it seems the OS simply "combines" more than one mouse/trackpad - any relative movement on those multiple mice is simply applied to the one mouse pointer, buttons are treated the same across all mice [though i've not tested if chording works across multiple mice, i.e. if i press right mouse button on one and left mouse button on the other if they're then counted as a chorded left-and-right mouse button press]).

Is it worth adding an informative note about this somewhere in 5.1.2.1? Just so that the above assumption and explanation of why there's only ever one mouse and it will always be isPrimary? Further, do we think there's ever going to be the possibility that a device/OS will allow multiple concurrent mice, and if so should we generalise the bullet list to determine the primary mouse, but then note that in practice there's only ever one mouse pointer?

[patrickhlauke]

/cc @RByers @jacobrossi

[RByers]

Yeah I think this is a good idea. Although it's rare, there are environments with multiple mouse cursors and there's no good reason for PE to prohibit that IMHO.