When using EXTR_PREFIX_ALL - and probably all the other EXTR_PREFIX_* constants - and a numerically-indexed array, extract() will add an underscore ("_") between the prefix and the index.
<?php
extract(array('foo', 'bar'), EXTR_PREFIX_ALL, 'var');
print_r(get_defined_vars()); // Reveals $var_0 = 'foo' and $var_1 = 'bar'
?>