Description:
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Tidy-PHP binding documentation is not very clear (yep, I will RTFS someday) but in each example uses the output $tidy object directly in an "echo" just to output it's value, using (I guess) it's internal __toString() method.
As far as I do "echo" it, no problem, but passing it to a string-accepting function actually converts it to a string instead of just using the output of its toString method.

Reproduce code:
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$tidy = tidy_parse_string('<b>Just a try', array(), 'UTF8');
$a = htmlspecialchars($tidy . '');
echo gettype($tidy) . ', ';
$a = htmlspecialchars($tidy);
echo gettype($tidy);

Expected result:
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Output: object, object

Actual result:
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Output: object, string