But thinking better, the "content" of the event being replied to should probably be readable if you want to enable this. As it will end up showing in "social" clients.
So if you have other metadata for the pull-request event put it on tags, and make "content" be a readable thing.
Makes sense for content to be readable or "viewable". I was thinking the content of a "PR" event or "source control context" event would be some sort of title first and perhaps a summary elsewhere.
Titles MAY be enumerated as "PR", "Issue", "Other" but could be left flexible to enable flexibility for how a client wants to structure the context around source control.
