PeachDrawing.Text
PeachDrawing.Text.Shaping.PlacedGlyph
PlacedGlyph.AttachedToIndex Property
For a mark that positioning attached to another glyph, the index of that glyph in the run; otherwise null. It is not kept on a run shaped for display in reverse order, where every glyph’s offset already accounts for the reversal.
public System.Nullable<int> AttachedToIndex { get; init; }