object/src/main/java/com/orientechnologies/orient/object/jpa/parsing/PersistenceXmlUtil.java
@Override
  public void startElement(String uri, String localName, String name, Attributes attributes) throws SAXException {
    PersistenceXml element = PersistenceXml.parse((localName == null || localName.isEmpty()) ? name : localName);
    schemaVersion = PersistenceXmlUtil.parseSchemaVersion(uri, element, attributes);
    // found, stop parsing
    if (schemaVersion != null) {
      throw new StopSAXParser();
    }

    // This should never occurs, however check if contain known tag other than TAG_PERSISTENCE
    if (TAG_PERSISTENCE != element && EnumSet.allOf(PersistenceXml.class).contains(element)) {
      throw new PersistenceException("Cannot find schema version attribute in <persistence> tag");
    }
  }
@Override
  public void startElement(String uri, String localName, String name, Attributes attributes) throws SAXException {
    PersistenceXml element = PersistenceXml.parse((localName == null || localName.isEmpty()) ? name : localName);
    schemaVersion = PersistenceXmlUtil.parseSchemaVersion(uri, element, attributes);
    // found, stop parsing
    if (schemaVersion != null) {
      throw new StopSAXParser();
    }

    // This should never occurs, however check if contain known tag other than TAG_PERSISTENCE
    if (TAG_PERSISTENCE != element && EnumSet.allOf(PersistenceXml.class).contains(element)) {
      throw new PersistenceException("Cannot find schema version attribute in <persistence> tag");
    }
  }
Fist tag of 'persistence.xml' (<persistence>) have to have 'version' attribute

@see org.xml.sax.helpers.DefaultHandler#startElement(java.lang.String, java.lang.String, java.lang.String,
org.xml.sax.Attributes)