* @throws XPathException if the prefix is prohibited
     */

    private void checkProhibitedPrefixes(String prefix, String uri) throws XPathException {
        if (prefix == null) {
            prefix = "";
        }
        if (uri == null) {
            uri = "";
        }
        if ("xmlns".equals(prefix)) {
            grumble("The namespace prefix 'xmlns' cannot be redeclared", "XQST0070");
        }
        if (uri.equals(NamespaceConstant.XMLNS)) {
            grumble("The xmlns namespace URI is reserved", "XQST0070");
        }
        if (uri.equals(NamespaceConstant.XML) && !prefix.equals("xml")) {
            grumble("The XML namespace cannot be bound to any prefix other than 'xml'", "XQST0070");
        }
        if (prefix.equals("xml") && !uri.equals(NamespaceConstant.XML)) {
            grumble("The prefix 'xml' cannot be bound to any namespace other than " + NamespaceConstant.XML, "XQST0070");
        }
    }