Represents the "Contents" entry of the page object object.
It is an optional entry defined as part of the PDF 1.0
It contains an array which contains StreamElements.
If you read the specification you will see that an array of one
may be represented as a single StreamElement rather
than an array. However we always present this property as an array
to simplify the interface. It is only if you add or remove items in
the array, that the underlying representation will be changed.
For definitive details see:.
The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 30,
Adobe Supplement to the ISO 32000, BaseVersion: 1.7,
ExtensionLevel: 3; Table: 3.27, page 23.
The ISO PDF
Specification, ISO 32000-2:2017 PDF 2.0; Table: 31, page 104.