Tracking issue for [RFC 326](https://github.com/rust-lang/rfcs/blob/master/text/0326-restrict-xXX-to-ascii.md). [Discussion](https://github.com/rust-lang/meeting-minutes/blob/master/weekly-meetings/2014-10-14.md#restrict-xxx-to-ascii)
