Improve documentation of `FT_Get_Track_Kerning'.
diff --git a/include/freetype/freetype.h b/include/freetype/freetype.h
index f6a6406..f41e27a 100644
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -2881,14 +2881,26 @@ FT_BEGIN_HEADER
/* */
/* point_size :: The point size in 16.16 fractional points. */
/* */
- /* degree :: The degree of tightness. */
+ /* degree :: The degree of tightness. Increasingly negative */
+ /* values represent tighter track kerning, while */
+ /* increasingly positive values represent looser track */
+ /* kerning. Value zero means no track kerning. */
/* */
/* <Output> */
- /* akerning :: The kerning in 16.16 fractional points. */
+ /* akerning :: The kerning in 16.16 fractional points, to be */
+ /* uniformly applied between all glyphs. */
/* */
/* <Return> */
/* FreeType error code. 0~means success. */
/* */
+ /* <Note> */
+ /* Currently, only the Type~1 font driver supports track kerning, */
+ /* using data from AFM files (if attached with @FT_Attach_File or */
+ /* @FT_Attach_Stream). */
+ /* */
+ /* Only very few AFM files come with track kerning data; please refer */
+ /* to the Adobe's AFM specification for more details. */
+ /* */
FT_EXPORT( FT_Error )
FT_Get_Track_Kerning( FT_Face face,
FT_Fixed point_size,