Creates an instance of TElMessagePartHandler class and returns a reference to newly created instance.
This method creates a new instance of TElMessagePartHandler class.
During the call of
IsSupportedThisBody class method, this method can set parameters for the instance, which will be created (if IsSupportedThisBody returns true). If Params is defined, then the newly created instance is responsible for destryoing it.
Params can be used to pass some data to the object being created. For example, if IsSupportedThisBody does some parsing of the data, then to avoid duplicate parsing in constructor, IsSupportedThisBody can put the parsed data to Params object.