We currently reject 'span' as a <custom-ident> only in grid-row/column. We should reject it in all line name lists too. https://drafts.csswg.org/css-grid/#typedef-line-names https://lists.w3.org/Archives/Public/www-style/2016Jun/0031.html https://drafts.csswg.org/css-values-3/#identifier-value (It /appears/ all names are valid in 'grid-template-areas' though: https://drafts.csswg.org/css-grid/#grid-template-areas-property since they are just strings with no additional restrictions, AFAICT. So, grid-template-areas:"inherit"; is a valid declaration, and grid-row:inherit-end; would match that area's end edge.)

If you haven't already started working on this, would it be all right if I co-opt this as a "good first bug" for an intern who starts in 2 weeks? (I could find another one as well; just pouncing on this one, since it fits the desired "good-first-bug" criteria of being a relatively small layout/style-system change, which affects behavior & is testable.)

Sorry, I already wrote the patch. It's a one-liner so probably a little bit too easy for an intern anyway.

Fair enough, no worries. (Let me know if you come across any other similarly-simple+testable changes that we need to make, which I can co-opt for an intern.)

I fixed a few of the existing invalid values in the test as well. I think we forgot to updated these when we switched from () to [] in the line name list syntax. https://treeherder.mozilla.org/#/jobs?repo=try&revision=603bf6d664f22c084dcd022aae3e2a374a9e783c

Pushed by mpalmgren@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/de7c0a103182 [css-grid] Make 'span' an invalid <custom-ident> in line name lists. r=dholbert

Updated: https://developer.mozilla.org/en-US/docs/Web/CSS/custom-ident and https://developer.mozilla.org/en-US/docs/Web/CSS/grid-row-start https://developer.mozilla.org/en-US/docs/Web/CSS/grid-row-end https://developer.mozilla.org/en-US/docs/Web/CSS/grid-column-start https://developer.mozilla.org/en-US/docs/Web/CSS/grid-column-end