1. A computer implemented XML parser for calling an external XML validator, said XML parser comprising: an XML receiver configured to receive an XML document from an XML application; an external XML validator caller configured to request the external XML validator to verify the validity of the XML document and to receive an answer to the request, wherein the external XML validator receives a schema or a DTD corresponding to the XML document in response to the request; and a DOM/SAX tree generator configured to generate, if said external XML validator caller receives an answer indicating that the XML document is valid, a DOM/SAX tree from the XML document and to transmit the DOM/SAX tree to the XML application.