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Editorial Team
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Asked: 2026-05-19T01:05:00+00:00

I’m trying create a regex that verifies an xml entity name is valid (see

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I’m trying create a regex that verifies an xml entity name is valid (see related issue: here).

(:|[A-Z]|_|[a-z]|[\xC0-\xD6]|[\xD8-\xF6]|[\xF8-\x2FF]|[\x370-\x37D]|[\x37F-\x1FFF]|[\x200C-\x200D]|[\x2070-\x218F]|[\x2C00-\x2FEF]|[\x3001-\xD7FF]|[\xF900-\xFDCF]|[\xFDF0-\xFFFD]|[\x10000-\xEFFFF])

Basically it’s verifying that the first character is a valid character. However the token [\xF8-\x2FF] is bombing out regex validation. Any idea why? I can’t figure it out.

UPDATE
The .net parser is throwing an exception that says range in reverse order.

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1 Answer

  1. Editorial Team

    You can only use one character per range in a regex and most regex parsers don’t understand multiple bytes using the \x notation. Use the \u notation instead.

    (:|[A-Z]|_|[a-z]|[\xC0-\xD6]|[\xD8-\xF6]|[\xF8-\u02FF]|[\u0370-\u037D]|[\u037F-\u1FFF]|[\u200C-\u200D]|[\u2070-\u218F]|[\u2C00-\u2FEF]|[\u3001-\uD7FF]|[\uF900-\uFDCF]|[\uFDF0-\uFFFD]|[\u10000-\uEFFFF])

    The .NET regex documentation states

    \x20 Matches an ASCII character using
    2-digit hexadecimal. In this case,
    \x2- represents a space.

    And for unicode:

    \u0020 Matches a Unicode character
    using exactly four hexadecimal digits.
    In this case \u0020 is a space.

    So I’ve used both above, \x for the 2-char hex values and \u for the larger ones.

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