<?xml version="1.0" encoding="UTF-8" ?> â€” This indicates that you have an XML file.
<Module> â€” This declares that this is a gadget.
<ModulePrefs title="Hello World!"> â€” This is the gadget information.
<Require feature="opensocial-0.8" /> â€” This indicates that you are using OpenSocial API version 0.8.
<Content type="html"> â€” This indicates that the gadget will be delivered as HTML. OpenSocial containers recommend this content type.