TBH I've never used this add-on so unsure whether there is an option for auto-tagging. You are probably best asking the author of the add-on or maybe post in resources requests for such an add-on though I suspect auto tagging will be an add-on you are going to have to pay to be developed if xentag doesn't have the feature your requiring.
Yes that's what I've had selected on a couple of occasions and it doesn't seem to be working for me. Think I missed some code edits during installation? (I didn't do any at all, just upload the files and XML).
I think I've figured out what that feature is. It links wording in your posts (all posts, first post, etc) to tags you've already made, automatically. But doesn't actually tag threads automatically. It's pretty cool. I think I've over-done it though my threads look like they belong to a seriously money-hungry skimlinks forum, where the adverts just go to tag pages. :/
I'll keep looking, or end up paying a developer I think.
Yep, wonderfull addon - tag essentials from @Daniel Hood
You can set predefinited tags per forum, so when user create thread, they will automaticall added to that thread, also it will use any tag from thread title too