A scrollable overlay with kinetic scrolling enabled may be hidden with opacity: 0; and shown later (using a HWA'd transition/animation). As such, you want to disable pointer interaction with the modal while it is hidden by using pointer-events: none;.
You will find that you cannot scroll the base page, because the user's pointer (finger) is still scrolling the invisible overlay.
That scrolling action should not be registered by the overlay, going to the next interaction-enabled element below.
Tracked by <rdar://problem/14735863>. iOS bugs are tracked internally, so closing this.
Here is a condensed test:
The darker "overlay" element is not scrollable in Safari/OS X, as expected. It scrolls in Safari/iOS, however, and blocks the "base" element's pointer input.
Test fails in iOS 8 GM.
Created attachment 280970 [details]
Comment on attachment 280970 [details]
Attachment 280970 [details] did not pass ios-sim-ews (ios-simulator-wk2):
New failing tests:
Created attachment 280972 [details]
Archive of layout-test-results from ews125 for ios-simulator-wk2
The attached test failures were seen while running run-webkit-tests on the ios-sim-ews.
Bot: ews125 Port: ios-simulator-wk2 Platform: Mac OS X 10.11.4
Created attachment 280973 [details]
Patch for landing
Comment on attachment 280973 [details]
Patch for landing
Clearing flags on attachment: 280973
Committed r201901: <http://trac.webkit.org/changeset/201901>
All reviewed patches have been landed. Closing bug.
(In reply to comment #9)
> Comment on attachment 280973 [details]
> Patch for landing
> Clearing flags on attachment: 280973
> Committed r201901: <http://trac.webkit.org/changeset/201901>
It broke the Apple Windows build, see build.webkit.org for details.
just to document, Alex already fixed it in https://trac.webkit.org/changeset/201915