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May 27, 2021 XML

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XML validation

DTD is the English Document Type Chinese meaning "document type definition."

XML with the correct syntax is called "good form" XML.

XML validated by DTD is "legitimate" XML.

A well-formed XML document

"In good form" XML documents have the correct syntax.

Grammar rules described in the previous section:

  • The XML document must have a root element
  • XML elements must have a close label
  • XML tags are case sensitive
  • XML elements must be properly nested
  • XML property values must be quoted
<?xml version="1.0" encoding="ISO-8859-1"?>
<body>Don't forget me this weekend!</body>

Validate the XML document

Legitimate XML documents are "in good form" XML documents, which also conform to the rules of 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>

In the example above, the DOCTYPE declaration is a reference to an external DTD file. The following paragraph shows the contents of this file.


The purpose of DTD is to define the structure of XML documents. It uses a series of legitimate elements to define the document structure:

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

If you want to learn DTD, please find the DTD tutorial on our home page.

XML Schema

W3C supports an XML-based DTD replacement 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 learn XML Schema, find the Schema tutorial on our home page.

A common XML validator

To help you check the syntax of XML files, we created an XML validator so that you can syntax check any XML file.

Take a look at the next chapter.

Related tutorials

DTD tutorial