Get the Code:
In this part of my XML Video Tutorial, I cover Document Type Definitions (DTD). DTDs are used to define the markup for your XML files.
We use DTD files to make sure data is valid and so multiple people can work together in a standardized way.
It sounds really complicated, but you are just defining what elements are required in the XML file and what type of data each element must have. The code at the link above will help you learn.