www.w3.org · w3c, spec, page-visibility-api · over 9 years ago
blogs.msdn.com · w3c, spec, learn, page-visibility-api, performance · almost 10 years ago
www.html5rocks.com · learn, page-visibility-api · over 10 years ago
blog.jasoncust.com · learn, javascript, page-visibility-api · about 11 years ago