This is for developers with an application written in a language like C, Java, etc., that want to be able to control Luup. The most common example would be a UPnP Control Point that will act as a remote control. Your application can talk to the Luup engine using standard the UPnP protocol, which consists of SOAP/XML requests. Additionally, Luup has a basic web server that will respond to the same commands when passed on a URL. This makes it easy to control Luup without knowing anything about UPnP. For example, to get the status of devices you can either use the UPnP action, which will return the status inside the SOAP response, or you can just open the URL: http://myip:49451/data_request?id=lu_status which is a shortcut to: http://myip:49451/data_request?id=lu_action&serviceId=urn:micasaverde-com:serviceId:HomeAutomationGateway1&action=GetStatus&output_format=json

You can specify on the URL the output_format, which is how you want to get the response back. This way you can make a UPnP Control Point entirely in java script or a perl script, for example, without needing to handle SOAP and XML. You can also read the main configuration file and modify it and actually replace Vera's built-in web user interface completely with your own.
For more information see: Luup Control