What will be the output of the following PHP code?<?php$var

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What will be the output of the following PHP code?

<?php
$var = 'vehicle';
$Res = filter_var($var, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);
echo $Res;
?>

1. Error
2. Null
3. True
4. False
5. None of these

Correct Option: B

There is an undocumented filter flag for FILTER_VALIDATE_BOOLEAN. The documentation implies that it will return NULL if the value doesn’t match the allowed true/false values. However this doesn’t happen unless you give it the FILTER_NULL_ON_FAILURE flag.