PeachDrawing.Text
PeachDrawing.Text.Shaping.PlacedGlyph
PlacedGlyph.IsHiddenIgnorable Property
Whether the glyph stands for a character that is invisible by definition and that the font draws nothing for: any variation selector, and another default-ignorable character (a joiner, a bidi control) the font has no glyph of its own for. Such a glyph takes part in substitution and positioning, so a lookup that matches on it still sees it, and is removed from the run at the end. A font that does map such a character keeps its glyph, which is drawn.
public bool IsHiddenIgnorable { get; init; }