RE: Directionality Standard

From: Murray Sargent (
Date: Wed Jan 09 2008 - 20:43:57 CST

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    Behnam, I have to admit that I'm tempted to agree with you. Unicode has run-level directionality format characters, e.g., RLM and LRM, but depends on a higher-level protocol for paragraph directionality. In working on the RichEdit engine over the years, I have run into situations where it would have been convenient to be able to specify the desired paragraph direction unequivocally in plain text. We even have a BiDi context feature that chooses the paragraph direction based on the first strong character encountered. Works the way you'd like most of the time.

    But I wonder how many display engines would break at this late date if we added paragraph directionality control characters. One scenario that comes to mind is copying an RTL paragraph to the plain-text slot on the clipboard. If an application prefixes the text with an RLPM (right to left paragraph mark), will target applications get confused and display a missing-character glyph? The same problem could occur with any unaware editor when opening a plain-text file containing an RLPM.

    So for a time at least, BiDi display would be messed up by the introduction of RLPM and LRPM format characters. One has to gauge whether the gain is worth the temporary confusion. If you stick with a higher-level text format like HTML, you don't have any problem.


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