Description:
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preg_split('/\s/', '') is used to split a string whose fields are delimited by whitespace chars. When the string is empty (""), preg_split returns a populated array rather than an empty array.

Expected: the equivalent in Perl returns an empty array (split(/\s/, '')).

Unexpected: preg_split in PHP returns a populated array.

Reproduce code:
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// Example 1 produces: Array ( [0] => )
$a = preg_split('/\s/', '');
print_r($a);

// Example 2 produces: Array ( [0] => )
$a = preg_split('/\s+/', '');
print_r($a);

// Example 3 produces: Array ( [0] => [1] => ) 
$a = preg_split('/\s*/', '');
print_r($a);

// Perl produces an empty array in all three cases.

Expected result:
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No output. Which is to say, the above code should be equivalent to PHP's:

$a = array();

Actual result:
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Array ( [0] => )
Array ( [0] => )
Array ( [0] => [1] => )