code: function(options) {
          options = options || {};
          this.params = {};
          this.headers = {};
          OpenLayers.Protocol.prototype.initialize.apply(this, arguments);
  
          if (!this.filterToParams && OpenLayers.Format.QueryStringFilter) {
              var format = new OpenLayers.Format.QueryStringFilter({
                  wildcarded: this.wildcarded,
                  srsInBBOX: this.srsInBBOX
              });
              this.filterToParams = function(filter, params) {
                  return format.write(filter, params);
              };
          }
      }
docs: Constructor: OpenLayers.Protocol.HTTP
  A class for giving layers generic HTTP protocol.
  
  Parameters:
  options - {Object} Optional object whose properties will be set on the
  instance.
  
  Valid options include:
  url - {String}
  headers - {Object}
  params - {Object} URL parameters for GET requests
  format - {<OpenLayers.Format>}
  callback - {Function}
  scope - {Object}