[css-grid] Why only <length>s in *-gap?

There was a question on Twitter [1] on why the *-gap properties didn’t allow percentages. I see some early discussion mentioning that the *-gap properties should allow <track-breadth> values minus the keywords, which would be <length> | <percentage> | <flex>. But the current draft only allows <length>s. Is there a reason for this?



Thanks,

Alan

[1] https://twitter.com/nilssolanki/status/712565981793619968