Represents the "BS" entry of the free text annotation object.

It is an optional entry defined as part of the PDF 1.6 specification.

It contains a BorderStyleElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 174, page 397.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 177, page 481.

The border style dictionary defines the line width and dash pattern for the annotation's outer border, used in preference to the legacy Border array when both are present.