Currently our parsing, style resolution and computed style implementation of grid-definition-{row|column} are pretty flat. The specification defines 4 production rules: <track-list> => [ [ <string> ]* <track-group> [ <string> ]* ]+ | none <track-group> => <track-minmax> | [ repeat( <positive-integer> , [ [ <string> ]* <track-minmax> [ <string> ]* ]+ ) ] <track-minmax> => minmax( <track-breadth> , <track-breadth> ) | auto | <track-breadth> <track-breadth> => <length> | <percentage> | <fraction> | min-content | max-content Aligning our implementation with that would make the code more readable and would be easier to add support for more of the syntax (minmax being my goal).