This is shelved for the moment - revisit later if it becomes an issue

At the moment, the Xsys functions can only take single combinations of input parameters.
It might be useful to allow for the calculation of multiple combinations of input combinations at once (a la CO2SYS.m).
However, algorithms currently identify parameters to be calculated by whether they are 'None' or not, so this would require a major re-tooling.

I reckon the effort involved here would be much greater than the inconvenience for the user having to run the function twice for different sets of input parameters.
How often do people actually use the ability of CO2SYS.m to take more than one combination of input parameters?