This may be a variation of the numerous overflow/clipping issues we've seen. However, even if that is the case, that is blocking this test from verifying the overflow behaves correctly following the column layout
The attached test has named flow content that flows through three regions that are children of an element that has a three-column layout. The content overflows both the third region and the multicol container.
Result: The content flows correctly through the three region columns, but the overflow is clipped
Expected: The overflow should be visible and it should flow into a fourth column. If I remove the regions and only test content overflowing the multicol container, it overflows into a fourth column.
Created attachment 210525 [details]
test file for bug
Created attachment 210526 [details]
reference file for test
The problem here is that a multicolumn container with a definite size should produce overflow columns if there is more content inside it than would fit in the definite size.
However, when the contents of the multicolumn container are regions, no overflow columns are generated *for the overflow* of the last region. That means that if the content in the last region will not overflow the region, overflow columns will be properly generated.
In order to observe the latter behavior, just add to the `#region-3` element in the attached sample, the declaration: `height: 400px;` - this will lead to the expected result being produced.
The test works with the old-multicol implementation. I'll investigate why it's not working with regions based multicol.
Created attachment 224502 [details]
Comment on attachment 224502 [details]
Created attachment 224847 [details]
Patch for landing
Comment on attachment 224847 [details]
Patch for landing
Clearing flags on attachment: 224847
Committed r164481: <http://trac.webkit.org/changeset/164481>
All reviewed patches have been landed. Closing bug.