Well, whichever lookahead is placed last doesn't need to be a lookahead, and the order doesn't matter as far as the result is concerned, so I could have written the pattern as follows: 
/
    ^
    (?=.*0)
    (?=.*1)
    (?=.*2)
    (?=.*3)
    (?=.*4)
    (?=.*5)
    (?=.*6)
    (?=.*7)
    (?=.*8)
    .{9}\z
/sx;

[download]

I figured it would be faster to check the length and for the presence of invalid characters first, and I left the last one as a lookahead for symmetry.

Note that this is basically the trick for doing "and" in regex matches. My original solution is roughly the same as 

/^[0-8]{9}\z/
&& /0/
&& /1/
&& /2/
&& /3/
&& /4/
&& /5/
&& /6/
&& /7/
&& /8/

[download]

In reply to Re^6: RegEx Question by ikegami
in thread RegEx Question by yoda54

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