Description:
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At https://www.php.net/manual/en/function.preg-replace.php it says
"As of PHP 7.0.0 E_WARNING is emitted in this case and "\e" modifier has no effect."

This implies that the results of the function should be the same whether or not the /e modifier is present.  But the actual result is that preg_replace returns null if the modifier is there regardless of the RE or the target string.

I have no particular problem with the behavior, but the documentation should reflect it.

Test script:
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$x = "1 2 3 a b c 4";

$y = preg_replace("#\d#e", 'X', $x));
$z = preg_replace("#\d#", 'X', $x));

//documentation implies that $y == $z