{"action":"created","issue":{"url":"https://api.github.com/repos/IDPF/epubcheck/issues/810","repository_url":"https://api.github.com/repos/IDPF/epubcheck","labels_url":"https://api.github.com/repos/IDPF/epubcheck/issues/810/labels{/name}","comments_url":"https://api.github.com/repos/IDPF/epubcheck/issues/810/comments","events_url":"https://api.github.com/repos/IDPF/epubcheck/issues/810/events","html_url":"https://github.com/IDPF/epubcheck/issues/810","id":276616814,"number":810,"title":"OPF : Undeclared prefix: 'a11y'","user":{"login":"garconvacher","id":24473413,"avatar_url":"https://avatars3.githubusercontent.com/u/24473413?v=4","gravatar_id":"","url":"https://api.github.com/users/garconvacher","html_url":"https://github.com/garconvacher","followers_url":"https://api.github.com/users/garconvacher/followers","following_url":"https://api.github.com/users/garconvacher/following{/other_user}","gists_url":"https://api.github.com/users/garconvacher/gists{/gist_id}","starred_url":"https://api.github.com/users/garconvacher/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/garconvacher/subscriptions","organizations_url":"https://api.github.com/users/garconvacher/orgs","repos_url":"https://api.github.com/users/garconvacher/repos","events_url":"https://api.github.com/users/garconvacher/events{/privacy}","received_events_url":"https://api.github.com/users/garconvacher/received_events","type":"User","site_admin":false},"labels":[{"id":60907001,"url":"https://api.github.com/repos/IDPF/epubcheck/labels/bug","name":"bug","color":"fc2929","default":true},{"id":705758022,"url":"https://api.github.com/repos/IDPF/epubcheck/labels/reviewed%20&%20ready%20for%20implementation","name":"reviewed & ready for implementation","color":"1d76db","default":false}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":7,"created_at":"2017-11-24T13:27:22Z","updated_at":"2018-02-01T09:42:22Z","closed_at":null,"author_association":"NONE","body":"Hi,\r\nthe metadata 'a11y' prefix in OPF occurs an error.\r\ne.g. `<meta property=\"a11y:certifiedBy\">` from [EPUB Accessibility Vocabulary](https://idpf.github.io/epub-vocabs/package/a11y/)\r\n\r\n"},"comment":{"url":"https://api.github.com/repos/IDPF/epubcheck/issues/comments/362211976","html_url":"https://github.com/IDPF/epubcheck/issues/810#issuecomment-362211976","issue_url":"https://api.github.com/repos/IDPF/epubcheck/issues/810","id":362211976,"user":{"login":"murata2makoto","id":5499496,"avatar_url":"https://avatars0.githubusercontent.com/u/5499496?v=4","gravatar_id":"","url":"https://api.github.com/users/murata2makoto","html_url":"https://github.com/murata2makoto","followers_url":"https://api.github.com/users/murata2makoto/followers","following_url":"https://api.github.com/users/murata2makoto/following{/other_user}","gists_url":"https://api.github.com/users/murata2makoto/gists{/gist_id}","starred_url":"https://api.github.com/users/murata2makoto/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/murata2makoto/subscriptions","organizations_url":"https://api.github.com/users/murata2makoto/orgs","repos_url":"https://api.github.com/users/murata2makoto/repos","events_url":"https://api.github.com/users/murata2makoto/events{/privacy}","received_events_url":"https://api.github.com/users/murata2makoto/received_events","type":"User","site_admin":false},"created_at":"2018-02-01T09:42:22Z","updated_at":"2018-02-01T09:42:22Z","author_association":"CONTRIBUTOR","body":">>I didn't see the a11y prefix is from the epub 3.1 specs.\r\n\r\n>Actually the prefix is defined in the EPUB Publications Reserved Prefixes document, which is a \"living document\". The \"a11y\" prefix was added while the WG worked on EPUB 3.1, but by being added there it should retroactively be allowed and pre-declared in EPUB 3.0.1 too (@mattgarrish correct me if I'm wrong).\r\n\r\nI think that addition of reserved prefixes is a mistake in EPUB 3.0.1.  In [Extending and Versioning Languages: Terminology](https://www.w3.org/2001/tag/doc/versioning), there is a definition of forwards compatibility.\r\n\r\n> A language change is forwards compatible if consumers of the unrevised language can correctly process all instances of the revised language.   \r\n\r\nI heard that Apple does not support the added prefixes.  I guess that they do not like this non-forwards compatible change."}}
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