If you refer to Example 8-1, you will notice that one of the parameters to the registry creation command was the identifier for the content endpoint for our gadget.
This specifies the endpoints in the device that we want to send content to. You can think of an endpoint as able to understand and display messages delivered to it in a particular format. This is directly analogous to ports on a TCP/IP device. A process behind a port is sent messages addressed to that port and knows what to do with them. As an example, a Web server behind port 80 is sent Hypertext Transfer Protocol (HTTP) requests and knows how to fetch Web page content and return it.
In the case of the endpoints for SideShow ...