Represents the "SpotFunction" entry of the type 1 halftone dictionary object.

It is a required entry defined as part of the PDF 1.0 specification.

This property may contain one of two different types:.

1) A string representing a PDF name object.

This item may take one of the following valid values:.

• SimpleDot
• InvertedSimpleDot
• DoubleDot
• InvertedDoubleDot
• CosineDot
• Double
• InvertedDouble
• Line
• LineX
• LineY
• Round
• Ellipse
• EllipseA
• InvertedEllipseA
• EllipseB
• EllipseC
• InvertedEllipseC
• Square
• Cross
• Rhomboid
• Diamond

2) A FunctionElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 130, page 309.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 128, page 371.