code: function inspectPrefiltersOrTransports( structure, options, originalOptions, jqXHR ) {
  
  	var inspected = {},
  		seekingTransport = ( structure === transports );
  
  	function inspect( dataType ) {
  		var selected;
  		inspected[ dataType ] = true;
  		jQuery.each( structure[ dataType ] || [], 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 selected;
  	}
  
  	return inspect( options.dataTypes[ 0 ] ) || !inspected[ "*" ] && inspect( "*" );
  }
docs: Base inspection function for prefilters and transports