The xml does not contain any predefined elements. Xml generally in broad terms is considered to be an architecture and not an application. Due to this reason it is not the responsibility of xml to specify how metadata is to be implemented. It is left up to the user to select how to implement metadata. Most browsers have their own way of specifying a method to handle metadata. The xml metadata interchange is used as a standard way for users to exchange information pertaining to metadata. The metadata information is usually stored in the form of attributes.
<body>Don't forget me this weekend!</body>
<body>I will not</body>
In the above code the id is used to identify different xml elements, this is also a form of metadata.