FYI: accidental/unwelcome IRI expansion

Dear all,

I recently brought up an issue to the JSON-LD mailing list <https://lists.w3.org/Archives/Public/public-linked-json/2015Dec/0004.html>, and they suggested that I notify this mailing list as well.

When learning Activity Streams 2.0 <http://www.w3.org/TR/2015/WD-activitystreams-core-20151006/>, I discovered that certain @ids were vulnerable to being mangled during JSON-LD expansion. For example, the absolute IRI tag:search.twitter.com,2005:347769243409977344 gets expanded to http://www.w3.org/ns/activitystreams#tagsearch.twitter.com,2005:347769243409977344 because tag is a term in the AS2 context. (The complete example is accessible with this JSON-LD Playground link <http://json-ld.org/playground/#startTab=tab-expanded&json-ld=%7B%22%40context%22%3A%22http%3A%2F%2Fwww.w3.org%2Fns%2Factivitystreams%22%2C%22%40id%22%3A%22tag%3Asearch.twitter.com%2C2005%3A593895901623496704%22%2C%22%40type%22%3A%22Create%22%2C%22url%22%3A%22http%3A%2F%2Ftwitter.com%2FKidCodo%2Fstatuses%2F347769243409977344%22%2C%22actor%22%3A%7B%22%40id%22%3A%22id%3Atwitter.com%3A2993982541%22%2C%22%40type%22%3A%22Person%22%2C%22displayName%22%3A%22Kid%20Codo%22%2C%22url%22%3A%22http%3A%2F%2Fwww.twitter.com%2FKidCodo%22%2C%22image%22%3A%22https%3A%2F%2Fsi0.twimg.com%2Fprofile_images%2F3664410292%2F1d75c213a572873bf6797c5591475da5_normal.jpeg%22%7D%7D>.)

-Josh Tilles

P.S. There was also a GitHub issue <https://github.com/jasnell/w3c-socialwg-activitystreams/issues/273> for this phenomenon.