[css3-exclusions] Issue 15183

This is an update to Issue 15183 (https://www.w3.org/Bugs/Public/show_bug.cgi?id=15183).

When reviewing the processing model with the co-editors of the spec we couldn't find any technical reason to keep this issue active. The issue statement is not correct since we do not require nor suggest that exclusions follow the CSS 2.1 absolute positioning. We simply don't forbid it and when used in that combination authors can achieve compelling typographic designs.

We propose resolving the issue as 'invalid'.

Thanks,
Rossen