code: protected boolean isValidQName(
          String prefix,
          String local,
          boolean xml11Version) {
  
          // check that both prefix and local part match NCName
          if (local == null)
              return false;
          boolean validNCName = false;
  
          if (!xml11Version) {
              validNCName =
                  (prefix == null || XMLChar.isValidNCName(prefix))
                      && XMLChar.isValidNCName(local);
          } else {
              validNCName =
                  (prefix == null || XML11Char.isXML11ValidNCName(prefix))
                      && XML11Char.isXML11ValidNCName(local);
          }
  
          return validNCName;
      }
docs: Taken from org.apache.xerces.dom.CoreDocumentImpl
  
  Checks if the given qualified name is legal with respect
  to the version of XML to which this document must conform.
  
  @param prefix prefix of qualified name
  @param local local part of qualified name