If sidebar.float.type is none, then no float is used.

If sidebar.float.type is before, then the float appears at the top of the page. On some processors, that may be the next page rather than the current page.

If sidebar.float.type is left or start, then a left side float is used.

If sidebar.float.type is right or end, then a right side float is used.

If your XSL-FO processor supports floats positioned on the inside or outside of double-sided pages, then you have those two options for side floats as well.