@property<EOL><INDENT>def source(self):<DEDENT>
return self._properties['<STR_LIT:source>']<EOL>
:returns: The originating system or interface that caused the event.  web for events caused by user action in the Twilio Console.  api for events caused through a request to the REST API.  twilio for events caused by an automated or internal Twilio system.
:rtype: unicode