RE: Directionality Standard

From: Jony Rosenne (
Date: Thu Jan 10 2008 - 00:00:22 CST

  • Next message: Murray Sargent: "RE: Directionality Standard"

    See Unicode Standard Annex #9, The Bidirectional Algorithm, clause 3.3.1.
    "The Paragraph Level".

    It seems there are many non-conforming applications out there, but the
    Unicode standard is clear and sufficient in this respect.


    -----Original Message-----
    From: [] On
    Behalf Of Murray Sargent
    Sent: Thursday, January 10, 2008 4:44 AM
    To: Behnam
    Cc: 'Waleed Oransa';;
    Subject: RE: Directionality Standard

    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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