[Honzo]

Ah I'm thinking of it wrong. The indexes are not the boxes but the splits in between.

| <- 0 1 -> | <- 1 2 -> | <- 2 3 -> |

That makes more sense.

[ahoy]

You're halfway there. The indices are the grid lines, but they're also one-indexed. That's consistent with other parts of CSS, though it's inconsistent with the rest of the programming world.

[goatlover]

Julia, R, Matlab, Basic and Fortran disagree.

It's just that C's heavy influence resulted in most languages with arrays being 0 indexed.

[fineline]

APL disagrees too. Except when it doesn't.