Description:
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DOMDocument::loadXML and DOMDocument::load raise undocumented PHP warnings when passed an empty string as the argument.

Reproduce code:
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$document = new DOMDocument();
$document->loadXML('');

Expected result:
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Since this is by design (see Bug #43809), the documentation should be updated to say what happens when you pass an empty string.

Something like:

"If an empty string is passed as the $source, a PHP warning will be generated. This warning is not generated by libxml and cannot be handled using libxml's error handling functions."