DTD - Elements

In a DTD, elements are declared with an ELEMENT declaration.

Declaring Elements

In a DTD, XML elements are declared with an element declaration with the following syntax:

<!ELEMENT element-name category>
or
<!ELEMENT element-name (element-content)>

Empty Elements

Empty elements are declared with the category keyword EMPTY:

<!ELEMENT element-name EMPTY>

Example:

<!ELEMENT br EMPTY>

XML example:

<br />

Elements with Parsed Character Data

Elements with only parsed character data are declared with #PCDATA inside parentheses:

<!ELEMENT element-name (#PCDATA)>

Example:

<!ELEMENT from (#PCDATA)>

Elements with any Contents

Elements declared with the category keyword ANY, can contain any combination of parsable data:

<!ELEMENT element-name ANY>

Example:

<!ELEMENT note ANY>

Elements with Children (sequences)

Elements with one or more children are declared with the name of the children elements inside parentheses:

<!ELEMENT element-name (child1)>
or
<!ELEMENT element-name (child1,child2,...)>

Example:

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

When children are declared in a sequence separated by commas, the children must appear in the same sequence in the document. In a full declaration, the children must also be declared, and the children can also have children. The full declaration of the "note" element is:

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

Declaring Only One Occurrence of an Element 

<!ELEMENT element-name (child-name)>

Example:

<!ELEMENT note (message)>

The example above declares that the child element "message" must occur once, and only once inside the "note" element.

Declaring Minimum One Occurrence of an Element

<!ELEMENT element-name (child-name+)>

Example:

<!ELEMENT note (message+)>

The + sign in the example above declares that the child element "message" must occur one or more times inside the "note" element.

Declaring Zero or More Occurrences of an Element 

<!ELEMENT element-name (child-name*)>

Example:

<!ELEMENT note (message*)>

The * sign in the example above declares that the child element "message" can occur zero or more times inside the "note" element.

Declaring Zero or One Occurrences of an Element 

<!ELEMENT element-name (child-name?)>

Example:

<!ELEMENT note (message?)>

The ? sign in the example above declares that the child element "message" can occur zero or one time inside the "note" element.

Declaring either/or Content

Example:

<!ELEMENT note (to,from,header,(message|body))>

The example above declares that the "note" element must contain a "to" element, a "from" element, a "header" element, and either a "message" or a "body" element.

Declaring Mixed Content

Example:

<!ELEMENT note (#PCDATA|to|from|header|message)*>

The example above declares that the "note" element can contain zero or more occurrences of parsed character data, "to", "from", "header", or "message" elements.

Get Your Diploma! W3Schools' Online Certification Program is the perfect solution for busy professionals who need to balance work, family, and career building. The HTML Certificate is for developers who want to document their knowledge of HTML, XHTML, and CSS. The ASP Certificate is for developers who want to document their knowledge of ASP, SQL, and ADO.

Jump to: Top of Page or HOME or Printer friendly page

W3Schools provides material for training only. We do not warrant the correctness of its contents. The risk from using it lies entirely with the user. While using this site, you agree to have read and accepted our terms of use and privacy policy.

Copyright 1999-2008 by Refsnes Data. All Rights Reserved.

W3Schools was converted to XHTML in December 1999