offsetSet should not be accessed directly, but instead used
via array access with the [] operator.
<?php
$p = new Phar('/path/to/my.phar', 0, 'my.phar');
try {
// calls offsetSet
$p['file.txt'] = 'Hi there';
} catch (Exception $e) {
echo 'Could not modify file.txt:', $e;
}
?>