I have released an update to my Picoformats plugin. This update changes the logic so that posts are not modified in the database (thanks, @aditya!), but on the fly. It will also link to the local profile/archive of a user (thanks, @als!) that has no URL set in their profile. Also, if you use an @ reply from inside a comment and use the (one-word) name of a comment poster, it will recognize this (if they have whitespace in their name, just take it out when writing the @ reply). @ replies in comments also do not check Twitter usernames anymore, since this is expensive and breaks common use.

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