HTML Whitelisting

Is there any guidance on how to properly use the markdown whitelister? In the many examples I’ve been searching through, I see things like: tag[attribute] but then there are also cases like tag.attribute being added as well. What is the difference between these? What effect does a wildcard have such as font[face=*] and are there other control characters you can use in here?

I also never see “class” whitelisted anywhere. Is this allowed by default? How does the system know when you are talking about whitelisting a class value instead of a separate attribute?