bliss's auto tagging feature runs a little different to its other features. Alongside being an auto tagger, bliss is a server application that applies rules to a music collection. These rules, however, tend to operate on tags within music files, so they are pretty useless for untagged files! That's why bliss's auto tagger runs alongside the rules; while the rules are fixing your already-tagged albums, the auto tagger can find metadata to tag inside your music files.
Unlike the rules in bliss, the auto tagger works without being configured. As soon as it sees an untagged music file it will run it through the auto tagger. Here's what the auto tagger actually does:
It's worth repeating that bliss auto-tags on a folder level basis. For all untagged files in a folder, it looks for information about a given release that all files appear on. This means it won't work for individual files stored in one folder. This is intentional; otherwise, bliss wouldn't know which release the file was in. If you think about popular songs, they aren't just in their original single release, they are also normally in an album and numerous compilations.
Technically speaking, bliss also treats certain tracks as untagged if they do have tags, but these tags are of a known value. These values are:
(That final one was a zero length string, i.e. if there's an album tag, but there's no actual data inside, it will be treated as untagged).
Note that bliss does not auto tag your music without your agreement. bliss presents all of the information it has found and allows a one-click Tag files operation.
So that's what bliss does and how it does it... now let's run bliss's auto tagger!