Table Spreadsheet Calculations

There is zero documentation on what kind of spreadsheet functionality works in XWiki tables. The only documented thing is SUM and it is also the only thing I can get to work. Even simple things like =(Address - Address) makes XWiki throw an exception on render. Is there documentation somewhere that explains what can be done in tables? Or is SUM about the, um, sum of it? I just wanted to have one cell subtracted from another cell... is this possible?