https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/UsingtheViewport/UsingtheViewport.html
https://dev.opera.com/articles/an-introduction-to-meta-viewport-and-viewport/
http://developer.blackberry.com/playbook/html5/documentation/viewport.html
https://developer.mozilla.org/en-US/docs/Mozilla/Mobile/Viewport_meta_tag?redirectlocale=en-US&redirectslug=Mobile%2FViewport_meta_tag
https://msdn.microsoft.com/en-us/library/windows/desktop/bb152361(v=vs.85).aspx
http://htmlref.com/
HTML5 Viewport Meta Tag
原文：http://www.cnblogs.com/geovindu/p/4954440.html
