code: def _base_body(self):
          
          item_attrib = {
              'xmlns:s': 'http://schemas.xmlsoap.org/soap/envelope/',
          }
          xml = XML.Element('s:Envelope', item_attrib)
  
          # Add the Header part
          XML.SubElement(xml, 's:Header')
          item_attrib = {
              'xmlns': 'http://www.sonos.com/Services/1.1'
          }
          credentials = XML.SubElement(xml[0], 'credentials', item_attrib)
          XML.SubElement(credentials, 'sessionId').text = self._session_id
          XML.SubElement(credentials, 'deviceId').text = self._serial_number
          XML.SubElement(credentials, 'deviceProvider').text = 'Sonos'
  
          return xml
docs: Return the base XML body, which has the following form:
  
          .. code :: xml
  
           <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
             <s:Header>
               <credentials xmlns="http://www.sonos.com/Services/1.1">
                 <sessionId>self._session_id</sessionId>
                 <deviceId>self._serial_number</deviceId>
                 <deviceProvider>Sonos</deviceProvider>
               </credentials>
             </s:Header>
           </s:Envelope>