Philippe Verdy wrote on 07/22/2003 09:18:35 PM: > If there's an agreement about what should have been the best > combining classes...
Describing what would be the best combining classes can be tricky for RTL scripts if the canonical ordering is intended not only for purposes of normalization and string comparison but also as a preferred order for storage and editing interaction. The reason is that the combining classes are intentionally based on visual relative position wrt the base character, not logical. Arbitrarily, a LTR ordering ... < below left < below < below right < ... is used, meaning that combinations of marks will be sequenced in the opposite order to the underlying line order, and so not in the logical order in terms of which users will be thinking. As an example using Hebrew, for a combination of (say) beth with qamats and dehi, preferred classes according to the visual basis on which classes are defined would be qamats = 220 dehi = 222 and so you'd get an encoded sequence of < beth, qamats, dehi >. But for the user, the pre-positive dehi, being to the right of the qamats, would probably be thought of as occuring before the qamats. Now, I said above that the classes were based arbitrarily on a visual LTR order. A RTL ordering ... < below right < below < below left < ... could have been used, but then the same mismatch would exist for LTR scripts. So, the problem is not with the arbitrary choice of LTR visual ordering for the classes. - Peter --------------------------------------------------------------------------- Peter Constable Non-Roman Script Initiative, SIL International 7500 W. Camp Wisdom Rd., Dallas, TX 75236, USA Tel: +1 972 708 7485
