Inverse rounded corners.
Example -- http://stackoverflow.com/questions/4012085/is-there-any-way-to-invert-a-rounded-corner-in-css
After many years of developers coming up with convulted solutions to give rounded corners it was implemented into CSS spec, now almost every (updated) site has rounded corners. It would be great to avoid using intensive JS libraries such as http://jquery.malsup.com/corner/ to achieve the inverse.
Chris, one appropriate forum to ask for features like this is the www-style mailing list. Would you mind submitting your idea there? Once features get accepted by the relevant working group then browser implementors are typically much happier about adopting them.
I'm going to close this bug for now. Reopen it or file a new one later if the CSSWG accepts the feature.
Shane, of course. Thanks for nudging me in the right direction.