@bender My point was that the suggested syntax for extending mentions to point to a specific message (<a href="/timeline/profile?url=url timestamp">@nick</a><a href="url timestamp" class="webmention"></a>) and having location based treading this way, might not break older clients, since they might just igonore the last value within the brackets.

@sorenpeter Unfortunately it does break all clients, because the original spec stated:

Mentions are embedded within the text in either @source.nick or @<source.url> format