How do you add extra per-forum setting fields?

[Marco van Herwaarden]

To add a string setting to the forum options, you would basicly need to do the following:
- Add column to the "forum" table. (add in install code, remove in uninstall code of the product)
- Create plugins to: Add a default (when adding a new forum, this could be skipped), Add the field to the edit page & add the column to the validfields.
- Create the phrases to use when editing the page

For a basic example, see this modification: Direct External Links
You will find all you need in there, without much extra stuff that could confuse things.