- an instance of Transport: actual transport object to be used
- a string: representing the class name of the object to be created
- a configuration array: the array must contain a class element which is treated as the object class,
and the rest of the name-value pairs will be used to initialize the corresponding object properties
- a PHP callable: either an anonymous function or an array representing a class method ([$class or $object, $method]).
The callable should return a new instance of the object being created.
