The :matrix property is a #GVariant property to specify where and what kind of white spaces to draw.
The #GVariant is of type "au", an array of unsigned integers. Each integer is a combination of #GtkSourceSpaceTypeFlags. There is one integer for each #GtkSourceSpaceLocationFlags, in the same order as they are defined in the enum (gtksource.types.SpaceLocationFlags.None and gtksource.types.SpaceLocationFlags.All are not taken into account).
If the array is shorter than the number of locations, then the value for the missing locations will be gtksource.types.SpaceTypeFlags.None.
By default, gtksource.types.SpaceTypeFlags.All is set for all locations.
Get matrix property.