data-* is an HTML5 attribute: http://dev.w3.org/html5/spec/Overview.html#embedding-custom-non-visible-data-with-the-data-attributes http://dev.w3.org/html5/spec

data-* is an HTML5 attribute: http://dev.w3.org/html5/spec/Overview.html#embedding-custom-non-visible-data-with-the-data-attributes http://dev.w3.org/html5/spec/Overview.html#embedding-custom-... The standard says that specific data-* attributes are only intended to be used by the site that generates the markup, but I think it's fair to say that an API using them can give semantic meaning to them for the use by any code using the API, without violating the standard.