<http://schema.org/about>
"The percentage of electricity generated in coal-fired power plants fell to its lowest level since 1978 at the end of last year."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.treehugger.com/fossil-fuels/2011-coal-produced-less-40-us-electricity-first-time-30-years.html>