Clarify role of EventListenerOptions in identifying handlers

[RByers]

It's not be entirely clear whether:

   addEventListener(type, handler);
   addEventListener(type, handler, {requiresCancelable: null});

Adds one event listener or two. Similarly, what about:

   addEventListener("scroll", handler, {requiresCancelable: false});
   addEventListener("scroll", handler, {requiresCancelable: null});

[tdresser]

This has implications on the shape of removeEventListener.

If two event handlers with distinct requiresCancelable values are considered the same, then no modification to removeEventListener is needed, and:

removeEventListener("scroll", handler)

should remove handler no matter what requiresCancelable is set to.

I think it would probably be simplest to be consistent with useCapture, and have your example add two event listeners. This preserves symmetry between addEventListener and removeEventListener, and consistency between the parameters to addEventListener.

[RByers]

Right, I wasn't even intending to question here whether requiresCancelable should participate in this, i.e. whether this should add one or two:

   addEventListener(type, handler, {requiresCancelable: true});
   addEventListener(type, handler, {requiresCancelable: false});

As defined at the moment that always adds two. I wrote it this way for the reason you mention - consistency among all options (although I did have an earlier proposal that omitted this and, as you say, didn't need to extend removeEventListener).

The subtler question is how exactly does the default value of requiresCancelable fit into this? Is unspecified the same as null (I think it should be)? Is null considered the same as false (or true) when they have the same semantics? Maybe issue #7 will address this.

[tdresser]

Is null considered the same as false (or true) when they have the same semantics?

That sounds confusing to me. I think null should be considered distinct from true and false, even if they have the same semantics (assuming we do go with a boolean).

I agree that unspecified should be the same as null.

[RByers]

What do you think of it now? There's technically a lot of changes necessary to the DOM spec to accommodate this, but I think this gets the point across now.

[tdresser]

This LGTM.