Question.....

A lot of popular TV Series' have fan novels that come after them. Star Trek, Babylon 5, Highlander, etc. They come out generally after the series is over, and go off in directions that sometimes it seems the series wouldn't go.

So my question is, are these part of canon or not? What makes me ask this is in the Highlander novels, a few characters are killed off. In stupid ways that make no sense. I don't consider any of that canon. Does anyone?