An order can be specified for:

Lower numbers place the tab earlier in the order, so -3 would be sorted before e.g. -2 and 1. A value of 0 is the default, so negative values put tabs in front and positive values after tabs in default location (tabs are in default location when they are not listed here - neither by specific name or by type - or are listed with value 0).

These can also be changed in the tab context menu.