XML Validation

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
<?xml version=”1.0″ encoding=”ISO-8859-1″?>
<body>Don’t forget me this weekend!</body>

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):

<?xml version=”1.0″ encoding=”ISO-8859-1″?>
<!DOCTYPE note SYSTEM “Note.dtd”>
<body>Don’t forget me this weekend!</body>

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:

<!DOCTYPE note
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT heading (#PCDATA)>

If you want to study DTD, you will find our DTD tutorial on our homepage.

XML Schema

W3C supports an XML-based alternative to DTD, called XML Schema:

<xs:element name=”note”>

<xs:element name=”to” type=”xs:string”/>
<xs:element name=”from” type=”xs:string”/>
<xs:element name=”heading” type=”xs:string”/>
<xs:element name=”body” type=”xs:string”/>


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.


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