Restrictions on values permitted for compartment `size` and `units` attributes.
Value of `spatialDimensions` | `size` allowed? | `units` allowed? | Allowable kinds of units | Default value of attribute `units`
--- | --- | --- | --- | ---
"`3`" | yes | yes | units of volume, or `dimensionless` | "`volume`"
"`2`" | yes | yes | units of area, or `dimensionless` | "`area`"
"`1`" | yes | yes | units of length, or `dimensionless` | "`length`"
"`0`" | no | no | (no units allowed) |