Description:
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PHP does not complain if you check for non-existant class with instanceof.

This provides space for subtle errors, like checking for DateRange when only Date_Range class is defined.

Test script:
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<?php
echo PHP_VERSION . "\n";
error_reporting(E_ALL);
class Foo {}
$a = new Foo;
// Notice that Bar class is never defined, however PHP does not complain about missing class.
if ($a instanceof Bar) { echo "Should be an error\n"; }
else { echo "PHP fail\n"; }

Expected result:
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Compiler error thrown saying that Bar was not found.

Actual result:
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Nothing happens.