Build 2.9.0.52 of xlsgen adds a forgotten and yet handy feature, the ability to decide where new worksheet tabs are created. So far, the only method for adding worksheet tabs to a spreadsheet was "AddWorksheet" which adds a new tab at the tail of existing tabs.

Sure, tabs can always be reordered, but why not let client applications choose where to put the new tabs in the first place?

Hence two new methods "AddWorksheetBefore" and "AddWorksheetAfter" which, as the names suggest, add new tabs respectively before and after the current worksheet. And that is the reason why the methods are exposed at the worksheet level, not at the workbook level.