serialize glyph names, clusters and positions.
serialize glyph extents.
serialize glyph flags. Since: 1.5.0
do not serialize glyph advances, glyph offsets will reflect absolute glyph positions. Since: 1.8.0
do not serialize glyph cluster.
do no serialize glyph name.
do not serialize glyph position information.
Flags that control what glyph information are serialized in hb_buffer_serialize_glyphs().