[css-images-4] image() fragment cannot be created from var()

[jsnkuhn]

The currently proposed image fragment syntax cannot be created from a css variable since css variables can't be used to create larger tokens.

Firefox's old -moz-image-rect syntax allows construction from css variables:
https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-image-rect

Codepen comparing -moz-image-rect() with the current proposed image():
https://codepen.io/jsnkuhn/pen/JjEpbwy?editors=1100

https://drafts.csswg.org/css-images-4/#image-fragments

[jsnkuhn]

maybe a fragment() function? Something similar to css clip-path like rect() or svg's viewbox() could be generalized for image fragment use?

[Loirooriol]

I guess #542 would allow this

[tabatkins]

Yup, this is basically a dup of #542