input-timestamps: Clarify interaction between relative-pointer and wl_pointer.frame

Should the wp_input_timestamps_v1.timestamp event be sent before a wp_relative_pointer_v1.relative_motion event?

The spec is not really clear on this:

The timestamp event is associated with the first subsequent input event carrying a timestamp which belongs to the set of input events this object is subscribed to.

Specifically this line the set of input events is obviously referring to base wl_pointer events, but does it also include extended events? Presumably so. Weston is the only compositor I know that implements the intput-timestamps protocol, and it doesn't send it.

Also how does this interaction occur within a single pointer frame? Say that a single pointer frame contains a relative motion event and regular motion event: Should the compositor send a timestamp event for each event like so?

wp_input_timestamps_v1.timestamp
wp_relative_pointer_v1.relative_motion
wp_input_timestamps_v1.timestamp
wl_pointer.motion
wl_pointer.frame

Or just one before both motion events? Because if a single frame has the same timestamp value across all events (which Weston, KDE, and Sway all do) then it doesn't make sense to do this. It would make more sense to clarify in the xml that a single frame has only one timestamp value provided across all contained events, and send a single wp_input_timestamps_v1.timestamp event once at the beginning of the frame for high res value.

Edit: Also related #88