These bidirectional attributes are associated with text output operations. The text output APIs in PM (WinDrawText and the various GpiCharString APIs) are sensitive to the presentation bidirectional attributes. These attributes are inherited from the process bidirectional attributes at creation time of each GPI presentation space.
The text-output APIs use the presentation bidi attributes to determine the conversions that must be applied to the text as part of the processing of the text-output APIs. For example, GpiCharString will convert bidirectional text, by calling the LayoutTransformText API on behalf of the application program. The bidi-converted string will then be rendered on the the output device (rather than the original string that has been provided in GpiCharString API call).
Applications can optionally modify the presentation bidi attributes dynamically by using the GpiSetBidiAttr API. Thus, applications have control on the text conversion that are executed on a call by call basis.