This comment is only partially correct:
"isValid() always returns false unless you enable checking for validity by $reader->setParserProperty(XMLReader::VALIDATE, true);"
This enables DTD checking, but you can also check by using RelaxNG (see setRelaxNGSchema() and setRelaxNGSchemaSource()).
And also, this is NOT correct:
"If you just need to check if XML file is well formed, successful loading into XMLReader object is usually enough."
It is not enough. Pull parsers operate on stream and if you have a large enough file they will not know it is well formed until it is read to the end. If you need to know if it is well formed or/and valid, read it till the end or validation error (you can use next() for fast reading if you don't care about contents).
XMLReader::isValid
(PHP 5 >= 5.1.2)
XMLReader::isValid — Indicates if the parsed document is valid
Descrição
XMLReader
bool isValid
( void
)
Returns a boolean indicating if the document being parsed is currently valid.
Valor Retornado
Retorna TRUE em caso de sucesso ou FALSE em falhas.
User Contributed Notes
XMLReader::isValid
XMLReader::isValid
anzenews at volja dot net
22-Jan-2008 04:50
22-Jan-2008 04:50
patryk dot szczyglowski at gmail dot com
21-Dec-2007 12:10
21-Dec-2007 12:10
isValid() always returns false unless you enable checking for validity by:
$reader->setParserProperty(XMLReader::VALIDATE, true);
where $reader is XMLReader object.
Beware, once you enable this check, PHP will search for DTD file and possibly produce warnings.
If you just need to check if XML file is well formed, successful loading into XMLReader object is usually enough.

XMLReader::getParserProperty