Type Alias Break 

pub type Break<'a> = &'a mut dyn FnMut(&mut Pdf, u32, Option<f32>) -> Location;

This returns a new Location because some collection elements need to keep multiple Locations at once (e.g. for page breaking inside of a horizontal list)

The second parameter is which location the break is occurring from. This number must be counted up for sequential page breaks. This allows the same page break to be performed twice in a row.

The third parameter is the height of the location.