{"action":"opened","issue":{"url":"https://api.github.com/repos/w3c/csswg-drafts/issues/2856","repository_url":"https://api.github.com/repos/w3c/csswg-drafts","labels_url":"https://api.github.com/repos/w3c/csswg-drafts/issues/2856/labels{/name}","comments_url":"https://api.github.com/repos/w3c/csswg-drafts/issues/2856/comments","events_url":"https://api.github.com/repos/w3c/csswg-drafts/issues/2856/events","html_url":"https://github.com/w3c/csswg-drafts/issues/2856","id":337403038,"node_id":"MDU6SXNzdWUzMzc0MDMwMzg=","number":2856,"title":"[css-grid] grid-line custom identifier auto?","user":{"login":"ewilligers","id":929206,"node_id":"MDQ6VXNlcjkyOTIwNg==","avatar_url":"https://avatars1.githubusercontent.com/u/929206?v=4","gravatar_id":"","url":"https://api.github.com/users/ewilligers","html_url":"https://github.com/ewilligers","followers_url":"https://api.github.com/users/ewilligers/followers","following_url":"https://api.github.com/users/ewilligers/following{/other_user}","gists_url":"https://api.github.com/users/ewilligers/gists{/gist_id}","starred_url":"https://api.github.com/users/ewilligers/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/ewilligers/subscriptions","organizations_url":"https://api.github.com/users/ewilligers/orgs","repos_url":"https://api.github.com/users/ewilligers/repos","events_url":"https://api.github.com/users/ewilligers/events{/privacy}","received_events_url":"https://api.github.com/users/ewilligers/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2018-07-02T07:41:03Z","updated_at":"2018-07-02T07:41:03Z","closed_at":null,"author_association":"CONTRIBUTOR","body":"Blink and WebKit reject grid-row-end `1 auto`.\r\nEdge and Firefox accept grid-row-end `1 auto` and serialize it as `1 auto`.\r\n\r\nBlink and WebKit reject grid-row-end values `span 1 auto`, `span auto 1` and `1 auto span`.\r\nEdge and Firefox accept these and serialize all of them as `span 1 auto`.\r\n\r\nTesting with uppercase makes it clear that `span` is being accepted as a keyword and `auto` is being accepted as a custom identifier:\r\nhttp://jsfiddle.net/ericwilligers/meya2q7d/\r\n\r\nAll browsers reject the following:\r\n`auto 1`\r\n`span span 1`, `span 1 span` and `1 span span`\r\n`1 span auto`, `auto 1 span` and `auto span 1`\r\n\r\n\r\n\r\nThe relevant grammar for `<grid-line>` is\r\n```\r\n<grid-line> =\r\n  auto |\r\n  <custom-ident> |\r\n  [ <integer> && <custom-ident>? ] |\r\n  [ span && [ <integer> || <custom-ident> ] ]\r\n```\r\n\r\nAre `auto` or `span` permitted as a `<custom-ident>`?\r\n\r\nThe [custom-ident spec](https://drafts.csswg.org/css-values-4/#identifier-value) may be relevant:\r\n\r\n> Note: When designing grammars with `<custom-ident>`, the `<custom-ident>` should always be \"positionally unambiguous\", so that it’s impossible to conflict with any keyword values in the property.\r\n\r\nI don't see a reading of the spec where `span 1 auto` would be permissible but not `span 1 span`.\r\n"}}
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