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To help search engines (like google) in generating "rich results" for your site, you can add a PageMap in the form of commented html-ish markup in your .
But how to know all the useful name-value that a search engine would use and would render as rich result? Is there an official list?
Google's official list of all the rich snippets that you can get is called the "search gallery":
When you say "PageMap/DataObject tags" I think you are referring to "structured data". The official site for all structured data is Schema.org. However, using most structured data will not lead to a rich snippet. It has to be listed in the search gallery for there to be a rich snippet associated with it.
