[\\u0600-\\u06FF]


\\ is a literal \ so I  that matches
 any one of characters \ u 0 6 F and all characters in the range  0 to \,
 except that 0 is char 48 and / is char 47 so this range is empty.


You don't need the u-notation to enter  code points into regexp (and
they don't work) as you can just enter the characters directly, or if
you want an ascii representation use xml character references, 
& # x a b c ;
These are not mentioned in the regex syntax as they are not really part
of that syntax they are expanded to the character by the XML parser
before XSLT starts.


> That's why I doubled the "\" character. Is this doubling spec-compliant ?

\\ is spec compliant but means a literal \.

David

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