How do I replace characters not in range [0x5E10, 0x7F35] with ‘*’ in PHP?

The following does the trick:

$str = "some മനുഷ്യന്റെ";

echo preg_replace('/[\x{00ff}-\x{ffff}]/u', '*', $str);
// some **********

echo preg_replace('/[^\x{00ff}-\x{ffff}]/u', '*', $str);
// *****മനുഷ്യന്റെ

The important thing is the u-modifier (see here):

This modifier turns on additional
functionality of PCRE that is
incompatible with Perl. Pattern
strings are treated as UTF-8. This
modifier is available from PHP 4.1.0
or greater on Unix and from PHP 4.2.3
on win32. UTF-8 validity of the
pattern is checked since PHP 4.3.5.

And here a short description why \uFFFF is not working in PHP:

Perl and PCRE do not support the
\uFFFF syntax. They use \x{FFFF}
instead. You can omit leading zeros in
the hexadecimal number between the
curly braces. Since \x by itself is
not a valid regex token, \x{1234} can
never be confused to match \x 1234
times. It always matches the Unicode
code point U+1234. \x{1234}{5678} will
try to match code point U+1234 exactly
5678 times.

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