KickStart Tutorial XML by Jan Kampherbeek - HTML preview

Valid XML documents

Valid

To be of practical use, an XML document needs to be valid. To be valid an XML document needs to apply to the following rules:
The document must be well formed. (More on well formed in the previous page).
The document must apply to the rules as defined in a Document Type Definition
(DTD), (More on DTD's in the next page)

If a document is valid, it's clearly defined what the data in the document really means.

There's no possibility to use a tag that's not defined in the DTD. Companies that exchange XML-documents can check them with the same DTD.
Because a valid XML document is also well formed, there's no possibility for typo's in the tags.

Valid is about structure

A valid XML-document has a structure that's valid. That's the part you can check. There's no check for the content.