Require non-cancelable events with "should" or "must" when there are only passive listeners

[zcorpan]

The spec allows non-cancellable events in https://w3c.github.io/touch-events/#cancelability

In particular, a user agent may generate only uncancelable touch events when it observes that there are no non-passive listeners for the event.

Why is this is only a "may", and not a "must" or at least "should"?

(This came up in web-platform-tests/wpt#34464 (comment) )

[patrickhlauke]

i believe some of the cautious language (should and may, rather than must) was a result of the history of this spec (and the fact that further development is only a CG draft report), which more or less retrospectively documented behavior done by Webkit (coupled with the fact that there was initially a bit of a PAG saber-rattling over the original 1.0 spec itself).

happy to go over the spec and make it more forceful where necessary.