for scripts not in their natural direction (eg. Latin in East gravity), choose per-script gravity such that every script respects the line progression. This means, Latin and Arabic will take opposite gravities and both flow top-to-bottom for example.
scripts will take their natural gravity based on the base gravity and the script. This is the default.
always use the base gravity set, regardless of the script.
PangoGravityHintdefines how horizontal scripts should behave in a vertical context.That is, English excerpts in a vertical paragraph for example.
See also [enum
Pango.Gravity]