This class represents the text markup annotation. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 179, page 403.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 182, page 489.

This class is always an indirect object because it inherits from MarkupAnnotationElement which is always an indirect object.

System.Object
    WebSupergoo.ABCpdf14.Elements.Element
       WebSupergoo.ABCpdf14.Elements.AnnotationElement
          WebSupergoo.ABCpdf14.Elements.MarkupAnnotationElement
             WebSupergoo.ABCpdf14.Elements.TextMarkupAnnotationElement

A text markup annotation highlights, underlines, strikes through, or squiggles a region of text. The specific visual effect is determined by the annotation Subtype: Highlight, Underline, StrikeOut, or Squiggly.

The QuadPoints entry defines the text region as a sequence of quadrilaterals, each enclosing one line of the marked text.