PHP: How to get schema validation error from XML reader?

I have a large XML file and I would like to use XMLReader for validating it against xsd schema.

I wrote the following code:

    $xmlReader = new XMLReader();
    libxml_use_internal_errors(true);
    $open = $xmlReader->open(APPLICATION_PATH.'/../public/Test feed from Charles.XML');
    $schema = $xmlReader->setSchema(APPLICATION_PATH.'/../public/schema/2.1/ONIX_BookProduct_Release2.1_reference.xsd');
    while($xmlReader->read()){
    }

    $errors = libxml_get_errors();
    $xmlReader->close();
    var_dump($errors);

Script output only one error, while file contains much more. How to correctly get validation error from XMLReader? Any working example will be very helpful.