`PangoDirection` represents a direction in the Unicode bidirectional algorithm.
Not every value in this enumeration makes sense for every usage of `PangoDirection`; for example, the return value of [ func@unichar_direction] and [func@find_base_dir] cannot be `PANGO_DIRECTION_WEAK_LTR` or `PANGO_DIRECTION_WEAK_RTL`, since every character is either neutral or has a strong direction; on the other hand `PANGO_DIRECTION_NEUTRAL` doesn't make sense to pass to [ func@itemize_with_base_dir].
The `PANGO_DIRECTION_TTB_LTR`, `PANGO_DIRECTION_TTB_RTL` values come from an earlier interpretation of this enumeration as the writing direction of a block of text and are no longer used. See `PangoGravity` for how vertical text is handled in Pango.
If you are interested in text direction, you should really use fribidi directly. `PangoDirection` is only retained because it is used in some public apis.