A caret position in a document's selectable text: between two glyphs of one page, counted in the page's reading order.
public TextPosition(int PageIndex, int Offset)
The zero-based page.
The number of glyphs before the caret on the page, in reading order: 0 is the page's start; an offset at or past the page's Length stands for its end.
ISO 32000-2 §14.8.2.5 (reading order). Spec #33 viewer capability 4.