Hmm, I see from the tests:

extent = (0.22, 1056.12, 7.43, 1101.567)
new_extent = nlmod.dims.snap_extent(extent, 10, 20)
assert new_extent == [-5.0, 1065.0, -10.0, 1110.0]

So the center of cells within the new extent is snapped to the closest multiple of delr/delc. I am more in favor of snapping the edge of cells to the closest multiple of delr/delc, like:

extent = (0.22, 1056.12, 7.43, 1101.567)
new_extent = nlmod.dims.snap_extent(extent, 10, 20)
assert new_extent == [0.0, 1060.0, 0.0, 1120.0]

Regis is also defined in intervals of 100 m, so from x = 100.000 until 100.100, x = 100.100 until 100.200 and so on. With your approach half of a cell would be in one regis-cell, and the other half would be in another one (if I am not mistaken).

I agree that makes a lot more sense

Two of the tests for the knmi data platform fail that are not related to this, I created an issue for this (#272) and will merge this PR.