low priority:

right now, it looks like idno's webmention handler uses the source query parameter as the source's canonical URL. no surprise there: most current webmention implementations do this, since they're almost always the same. http://brid.gy/ is one case where they're different, though, and in that case the u-url property should take precedence (i hope).

e.g. bridgy generated the likes and retweets on http://werd.io/2014/why-i-love-silicon-valley-despite-hating-silicon-valley#comments, and the permalinks all point to brid.gy, but they should ideally point to the twitter.com links in the u-urls instead.