An exception is a part of many user-fixes which defines certain parts of your wiki where you do not wish the replacements defined by the fix to be applied.
Scroll down to the bottom of Fix:SpellBot to see how and where exceptions are placed within a fix.
There are many types of exception, and this list is not exhaustive.
|inside-tags||anything between the HTML tags given is ignored||if you're running a British spell checker, you probably want to have an exception for the tags 'div' and 'span', since these tags often contain and require the American spelling of color and center|
|category||ignores all pages in the category you specify||if your fix changes Image: to File:, you'll probably want to ignore category:Help, since this is likely where you've got a page explaining why useing File: is better markup than Image:|
|inside||basically means "inside the page". But it's kind of the reverse of other exceptions. It means to except the things defined on every page.||If you have a spell-checking user-fix, this is where you put the words you don't want spellchecked. Again, this is not the pages that you don't want spellchecked, but the individual strings on the page that you don't want touched.|