Represents the "Start" entry of the dpart dictionary object.

It is defined as part of the PDF 2.0 specification.

It contains a PageObjectElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 409, page 830.

The Start entry references the first page object of the page range belonging to this document part. Together with End it defines the contiguous page range covered by the part.