Description:
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The documentation page for SplFileObject::__construct():
http://uk1.php.net/manual/en/splfileobject.construct.php

Says:
Throws a RuntimeException if the filename cannot be opened.

Which is true as long as the file does not exist.
However, the test script below shows that when $filename is a directory, it's 
actually a LogicException that's thrown.

The documentation thus needs to be changed as follows:

Throws a RuntimeException if the filename cannot be opened.
Throws a LogicException if the filename is a directory.

Test script:
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new SplFileObject('.');

Expected result:
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RuntimeException

Actual result:
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LogicException: Cannot use SplFileObject with directories