If you would like to force the API to provide the XML version you need to change the parameter format to format=xml.
Another option to switch between the two output formats is the Accept parameter send to the server in the header of the HTML request. The screenshot below shows the typical XML output (top part of the figure) and parts of the request header (bottom). Besides the typical text/html format, the request asks for application/xml as one output option. If this is changed to application/json the API will send the answer in JSON format.
If you would like to try it yourself you can use the Firefox addon Modify Headers.
We hope you will find the new feature useful. Every feedback is very welcome.