PRI 57 - Changes to Bidi categories of some characters used with Mathematics

From: Uri Bernstein (
Date: Sun Oct 02 2005 - 03:07:39 CST

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    I recently became aware of some changes made in Unicode 4.1.0 to the
    bidi categories of some characters, most noticeably U+2212 MINUS SIGN.
    These changes were presented as PRI 57, and approved on 2005-02-14.

    Unfortunately, this change made it impossible to embed negative
    numbers (such as "-5") in right-to-left text, without resorting to
    bidi control characters.
    After the bidi category of HYPHEN-MINUS was changed (between 4.0 and
    4.0.1), that character could no longer be used any more as a unary
    minus in RTL text. However, there was a solution: using MINUS SIGN
    instead. But with this recent change, even this no longer works.

    I would like to know what was the reasoning behind the changing the
    category of MINUS SIGN. I would also like to know what is currently
    the recommended way of embedding a negative number in RTL text.

    Uri Bernstein

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