From: "Andrew C. West" <[EMAIL PROTECTED]> (...) > As has been stated time and time again, mixing vertical and horizontal textual > orientation in the same document is beyond the scope of a plain text standard, > and rendering mixed horizontal/vertical text is certainly beyond the ability of > any plain text editor that I know of. Markup is the appropriate way to deal with > mixed horizontal/vertical/diagonal/circular/spiral text (Artemis Fowl has a > constructed "script" with spiral textual orientation), not dozens of new > directional control characters.
What about boustrophedon? Isn't there also some vertical boustrophedon layout, i.e. TTB and BTT alternated on each vertical row? My opinion is that, whatever the directionality used, it does not matter. Bidi character properties are only useful when handling local changes of directionality within the same document, so that they require reordering when rendering mixed scripts, before the final main directionality is applied (this final main directionality could use horizontal/vertical rows or whatever, and the direction of rows can be contant or alternated; it does not matter and this is out of scope of Unicode encoding). LRO/LRM/BDE controls and so on are to be used to override the main direction of characters belonging to the same script, when they are used in contexts where the main direction must be escaped. BiDi character properties are there to avoid using these controls when they are not necessary. If something is not specified in BiDi properties, then the characters will be laid out according to the (out of Unicode scope) document directionality. May be this should be clarified in the Unicode spec, so that these controls and properties are defined in terms of "character direction" (the second "row direction" will not be encoded, allowing boustrophedon or unidirectional layouts), instead of just "left" and "right". The wellknown exception to this directionality model is Hangul whose clusters adopt a local horizontal/vertical for rendering their composite jamos in the same syllable. If leading and trailing consonnants had not been encoded separately, one would need to encode a special punctuation to mark syllable boundaries. (This punctuation would not necessarily have a visible glyph, it could be a thin space or an arrangement of the text layout, in the traditional Hangul squares). In Hangul, syllables breaks are marked by the layout, but not word breaks; in Latin/Greek/Cyrillic/Hebrew this is the reverse, and I consider SPACE as a punctuation; either word breaks or syllable breaks are needed to make the text readable, i.e. less ambiguous, to reflect the speech and common semantics of words where these breaks are often heard and needed too. If this Hangul layout was better understood, and implemented as a layout feature, one could easily see that Hangul is extremely simple and regular, and has very few letters. (for example SSANGSIOS is currently encoded distinctly from SIOS,SIOS, despite the two are identical semantically and should be rendered identically, unless one is a trailing consonnant and the other a leading one, in which case their separation is either marked in the layout by a cluster boundery, or by an explicit punctuation which could as well be a thin space character or a small dot mark). The current encoding of Hangul ignores this feature, and makes handling Hangul unnecessarily complicate, when all could be handled as a strict encoding of an "horizontal" row of text, with a special layout to compose squares. Square-layout does not seem mandatory in Hangul, and Koreans can also read text rendered with uniform halfwidth and unidirectional jamos, making it a true alphabet. Vertical presentation is also common for this, and readers that already can read text horizontally or vertically would read without much problems a boustrophedon layout, or featured layouts like spiral, circular, provided that glyph orientation is kept recognizable. I see the square layout only as the prefered layout for Koreans, as it fits well with Han characters and with its long strong tradition for presentation. Han ideographs also have a square layout of strokes. But they are a bit more complex because they use many featured ligatures, so that strokes take some contextual shapes depending on surrounding strokes and the number of strokes in the square (these make the ideographs more readable, by a more uniform distribution of blackness and stroke widths within the square, or by enhancing the symetries and parallelisms). On the opposite, the limited set of letters (strokes) in Hangul and the absence of overlays makes the rendering task much easier within squares.
