I think what confuses the issue it the misleading symmetry between the terms LTR and RTL.
If Hebrew and Arabic were simply written from right to left there would be no need for a bidi algorithm and the direction would be a simple presentation issue. However, in Hebrew and Arabic, numbers are written left to right and so are Latin and other LTR script quotations. So RTL really means mixed direction, and the bidi algorithm is there to handle it automatically with little user intervention. All of this is completely irrelevant to boustraphedon and vertical scripts. These are presentation issues that have not need for Unicode support. Jony
