to switch between two different modes of rendering.
to author with specific requirements and/or semantics
to convert from one version to another one
to create helping tool for authoring document
to validate
to evolve the semantics of elements and attributes
看起來跟這個有關係 http://www.zhihu.com/question/20527726
http://www.w3.org/QA/2007/05/html_and_version_mechanisms.html
People are requesting a version number to be able
to switch between two different modes of rendering. to author with specific requirements and/or semantics to convert from one version to another one to create helping tool for authoring document to validate to evolve the semantics of elements and attributes
正解 再也不敢用禁止广告插件了