typedef uint32_t GlyphIndex; ///< An index into an array of glyphs.
typedef uint32_t ScriptRunIndex; ///< An index into an array of script runs.
typedef uint32_t FontRunIndex; ///< An index into an array of font runs.
+typedef uint32_t UnderlineRunIndex; ///< An index into an array of underline runs.
typedef uint32_t BidirectionalRunIndex; ///< An index into an array of font runs.
typedef uint32_t LineIndex; ///< An index into an array of lines.