code: function(config) {
          config = OpenLayers.Util.extend(config, {method: "POST"});
          // set content type to application/xml if it isn't already set
          config.headers = config.headers ? config.headers : {};
          if(!("CONTENT-TYPE" in OpenLayers.Util.upperCaseObject(config.headers))) {
              config.headers["Content-Type"] = "application/xml";
          }
          return OpenLayers.Request.issue(config);
      }
docs: APIMethod: POST
  Send a POST request.  Additional configuration properties are
  documented in the <issue> method, with the method property set
  to POST and "Content-Type" header set to "application/xml".
  
  Parameters:
  config - {Object} Object with properties for configuring the request.
  See the <issue> method for documentation of allowed properties.  The
  default "Content-Type" header will be set to "application-xml" if
  none is provided.  This object is modified and should not be reused.
  
  Returns:
  {XMLHttpRequest} Request object.