- Document Type Definition (DTD) can be included to specify the allowed structuring
- Returning to our exam paper example:
- The <exam> element is the root element
- There can be one or more questions followed by answer pairs
- Each <question> element is followed by an <answer>
- The <exam> element has attributes author and paper
If the document references a DTD and matches
the DTD, it is called a valid document
All valid documents are well-formed