XML with correct syntax is "Well Formed" XML.
XML validated against a DTD is "Valid" XML.
Well Formed XML Documents
A "Well Formed" XML document has correct XML syntax.
The syntax rules were described in the previous chapters:
- XML documents must have a root element
- XML elements must have a closing tag
- XML tags are case sensitive
- XML elements must be properly nested
- XML attribute values must be quoted
Valid XML Documents
A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):
The DOCTYPE declaration in the example above, is a reference to an external DTD file. The content of the file is shown in the paragraph below.
The purpose of a DTD is to define the structure of an XML document. It defines the structure with a list of legal elements:
If you want to study DTD, you will find our DTD tutorial on our homepage.
W3C supports an XML-based alternative to DTD, called XML Schema:
If you want to study XML Schema, you will find our Schema tutorial on our homepage.
A General XML Validator
To help you check the syntax of your XML files, we have created an XML validator to syntax-check your XML.
Please see the next chapter.