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]
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Answer 1

For systems that internally stores the codepoints in UTF-16, it is common to use surrogate pairs (xD800-xDFFF) for codepoints above 0xFFFF and in those systems you must verify if you really can use for example \u12345 or must specify that as a surrogate pair. (I just found out that in C# you can use \u1234 (16 bit) and \U00001234 (32-bit))

According to Microsoft "the W3C recommendation does not allow surrogate characters inside element or attribute names." While searching W3s website I found C079 and C078 that might be of interest.