Description:
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Array keys in PHP 6 differentiate between unicode and binary strings - that is, a unicode key of 'test' is entirely different than a binary key of 'test'.

Reproduce code:
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$arr = array();
$arr[ (unicode)'test' ] = 'unicode';
$arr[ (binary)'test' ] = 'binary';

// If unicode semantics is enabled, this will output 'unicode'
var_dump( $arr['test'] );

// Will output 'binary'
var_dump( $arr[ b'test'] );

// Will output 'unicode'
var_dump( $arr[ (unicode)'test' ] );

Expected result:
----------------
All three lines should output 'binary'

unicode(7) "binary"
unicode(6) "binary"
unicode(7) "binary"

Actual result:
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unicode(7) "unicode"
unicode(6) "binary"
unicode(7) "unicode"