[css-grid] Specified value of grid-auto-flow

[fantasai]

There's a WPT test (grid-auto-flow-valid.html) that requires the specified value row dense to serialize as dense, but it's not clear to me that the spec supports dropping this keyword... it also would create a problem if we change the initial value to a more automatic keyword like normal, because then row dense and dense are not equivalent. (Also having column dense and row dense behave consistently is kinda nice, if I'm being honest.)

[Loirooriol]

it's not clear to me that the spec supports dropping this keyword

It's as per https://drafts.csswg.org/cssom/#serializing-css-values :

If component values can be omitted or replaced with a shorter representation without changing the meaning of the value, omit/replace them.

[cdoublev]

But it also requires not omitting it if it would be less backward compatible. I think specs should clearly state when a component value cannot be omitted in order to preserve back-compat.

[Loirooriol]

Well yes, but all browsers are dropping the keyword. So the back-compat exception doesn't apply.