Unicode Regex; Invalid XML characters

Question

The list of valid XML characters is well known, as defined by the spec it's:

#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF] 

My question is whether or not it's possible to make a PCRE regular expression for this (or its inverse) without actually hard-coding the codepoints, by using Unicode general categories. An inverse might be something like [\p{Cc}\p{Cs}\p{Cn}], except that improperly covers linefeeds and tabs and misses some other invalid characters.

Answer 1

I know this isn't exactly an answer to your question, but it's helpful to have it here:

Regular Expression to match valid XML Characters:

[\u0009\u000a\u000d\u0020-\uD7FF\uE000-\uFFFD] 

So to remove invalid chars from XML, you'd do something like

// filters control characters but allows only properly-formed surrogate sequences private static Regex _invalidXMLChars = new Regex(     @"(?<![\uD800-\uDBFF])[\uDC00-\uDFFF]|[\uD800-\uDBFF](?![\uDC00-\uDFFF])|[\x00-\x08\x0B\x0C\x0E-\x1F\x7F-\x9F\uFEFF\uFFFE\uFFFF]",     RegexOptions.Compiled);  /// <summary> /// removes any unusual unicode characters that can't be encoded into XML /// </summary> public static string RemoveInvalidXMLChars(string text) {     if (string.IsNullOrEmpty(text)) return "";     return _invalidXMLChars.Replace(text, ""); } 

I had our resident regex / XML genius, he of the 4,400+ upvoted post, check this, and he signed off on it.