code: function inspectPrefiltersOrTransports(structure, options, originalOptions, jqXHR) {
  
      var inspected = {},
          seekingTransport = structure === transports;
  
      var inspect = function inspect(dataType) {
          var selected = undefined;
          inspected[dataType] = true;
          //jQuery.each( structure[ dataType ] || [], function( _, prefilterOrFactory ) {
          (structure[dataType] || []).every(function (prefilterOrFactory) {
              var dataTypeOrTransport = prefilterOrFactory(options, originalOptions, jqXHR);
              if (typeof dataTypeOrTransport === "string" && !seekingTransport && !inspected[dataTypeOrTransport]) {
                  options.dataTypes.unshift(dataTypeOrTransport);
                  inspect(dataTypeOrTransport);
                  return false;
              } else if (seekingTransport) {
                  return !(selected = dataTypeOrTransport);
              }
              return true;
          });
          return selected;
      };
  
      return inspect(options.dataTypes[0]) || !inspected["*"] && inspect("*");
  }
docs: Base inspection function for prefilters and transports