Represents the "TI" entry of the list field object.

It is an optional entry defined as part of the PDF 1.0 specification.

It contains an integer representing a PDF numeric object.

The PDF specification states that this item assumes a value of 0 if no value has been provided.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 231, page 445.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 234, page 539.

The top index scrolls the list display to show the option at this zero-based index at the top of the visible area.