Encyclopedia encloses information for us especially we wanna have a glimpse of something that we're not sure of. A reference, more or less is needed when it comes to assuage our mind's hunger for knowledge.
When it comes to HTML, probably there are some HTML elemets that we've overlooked or left forgotten. If you need references regarding HTML elements - check out this 'Encyclopedia of HTML elements' starts from A-to-V (not A-to-Z). It makes HTML writing a bit easier - of course, thru references - we can't recall that much!) ;)