at

There is another page with same name:

@

at

[1] http://purl.org/atompub/tombstones/1.0 は、 at:deleted-entry 要素の名前空間URLです。

仕様書

[2] RFC 6721 - The Atom "deleted-entry" Element (2012-12-31 01:08:20 +09:00 版) <http://tools.ietf.org/html/rfc6721#section-2>