Description:
------------
The tidy::getOptDoc() manual page notes[1]:

| You need at least libtidy from 25 April, 2005 for this function
| be available.

However, the official Windows PHP 7.1.23 distribution does neither
support this method nor its procedural pendant tidy_get_opt_doc(),
even though it ships with libtidy 5.4.0 (2017/03/01).

[1] <http://php.net/manual/en/tidy.getoptdoc.php>

Test script:
---------------
<?php
$tidy = new tidy;
echo $tidy->getOptDoc('tidy-mark');
?>

Expected result:
----------------
This option specifies if Tidy should add a <code>meta</code>
element to the document head to indicate that the document has
been tidied. <br/>Tidy won't add a meta element if one is already
present.

Actual result:
--------------
Fatal error: Uncaught Error: Call to undefined method tidy::getOptDoc() in […]