This property represents the first parameter associated with the destination.

The number of parameters and purpose of each varies depending on the EntryType of the Destination.

However in general they represent coordinates on the page which need be visible or aligned in some way.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 151, page 366.

The second parameter of the destination. For XYZ it is the top edge coordinate; for FitV and FitBV it is the left edge coordinate; for FitR it is the bottom edge of the fit rectangle.