No unit exponent restrictions

In SBML Level 2, the attribute exponent on Unit was defined to be of type int. In Level 3, the range of values will unrestricted by changing the data type to double. This change is a consequence of the decision that the spatial dimensions of Compartment objects should be allowed to be non-integer values.

Changes compared to Level 2

The figure below shows the definition of Unit and UnitDefinition in Level 3 Core. The data type of the exponent attribute is now a double.

Notable implications

This change should be completely forward-compatible with Level 2: any value for the exponent attribute used in a valid SBML Level 2 model will be valid in Level 3 Core.