5 Rarely Used HTML Elements

I saw this post on 5 rarely used HTML tags:

• "address""for address fields ",
• "q" for double or single quotation (does not seem to work with IE),
• "optiongroup" to group options,
• "acronym" or "abbr"for abbreviations and
• "optiongroup" & "legend" for grouping items inside a form.
  

Seemed pretty useful to me.