Elements are labels used to describe your content. They're described in the DTD by element declarations and invoked in the document element as tags. Element declarations by default define tag pairs. Tag pairs contain text as well as other elements and their content. An element declaration may also define an empty element, one that isn't designed to contain any text or other elements.
Attributes provide extra information about the element.
One of the rules of XML is that all attribute values, regardless of type must be enclosed in quotation marks. Attributes are not expandable. Attributes are more difficult to manipulate by program code. The last line defines the end of the root element. The empty platform and os elements have a slash before the greater than sign that closes the tag.