public function serializeEnvelope($body, $headers = false, $namespaces = array(), $style = 'rpc', $use = 'encoded', $encodingStyle = 'http://schemas.xmlsoap.org/soap/encoding/')
    {
        // TODO: add an option to automatically run utf8_encode on $body and $headers
        // if $this->soap_defencoding is UTF-8.  Not doing this automatically allows
        // one to send arbitrary UTF-8 characters, not just characters that map to ISO-8859-1

        $this->debug("In serializeEnvelope length=" . strlen($body) . " body (max 1000 characters)=" . substr($body, 0, 1000) . " style=$style use=$use encodingStyle=$encodingStyle");
        $this->debug("headers:");
        $this->appendDebug($this->varDump($headers));
        $this->debug("namespaces:");
        $this->appendDebug($this->varDump($namespaces));

        // serialize namespaces
        $ns_string = '';
        foreach (array_merge($this->namespaces, $namespaces) as $k => $v) {
            $ns_string .= " xmlns:$k=\"$v\"";
        }
        if ($encodingStyle) {
            $ns_string = " SOAP-ENV:encodingStyle=\"$encodingStyle\"$ns_string";
        }

        // serialize headers
        if ($headers) {
            if (is_array($headers)) {
                $xml = '';
                foreach ($headers as $k => $v) {
                    if (is_object($v) && get_class($v) == 'soapval') {
                        $xml .= $this->serialize_val($v, false, false, false, false, false, $use);
                    } else {
                        $xml .= $this->serialize_val($v, $k, false, false, false, false, $use);
                    }
                }
                $headers = $xml;
                $this->debug("In serializeEnvelope, serialized array of headers to $headers");
            }
            $headers = "<SOAP-ENV:Header>" . $headers . "</SOAP-ENV:Header>";
        }
        // serialize envelope
        return
            '<?xml version="1.0" encoding="' . $this->soap_defencoding . '"?' . ">" .
            '<SOAP-ENV:Envelope' . $ns_string . ">" .
            $headers .
            "<SOAP-ENV:Body>" .
            $body .
            "</SOAP-ENV:Body>" .
            "</SOAP-ENV:Envelope>";
    }