Rules for Creating Document Type Definition, or DTD, Elements

Basically, you prepare and use a Document Type Definition (DTD) to add structure and logic, making it easier to ensure that all essential features are present — in the right order — in your XML document. You may develop many rules in your DTD that control how elements can be used in an XML document.

Symbol	Meaning	Example
#PCDATA	Contains parsed character data or text	<element (#PCDATA)>
#PCDATA, element-name	Contains text and another element; class="code">#PCDATA is always listed first in a rule	<element (#PCDATA, child)*>
, (comma)	Must use in this order	<element (child1, child2, child3)>
| (pipe bar)	Use only one element of the choices provided	<element (child1 | child2 | child3)>
element-name (by itself)	Use one time only	<element (child)>
element-name?	Use either once or not at all	<element (child1, child2?, child3?)>
element-name+	Use either once or many times	<element (child1+, child2?, child3)>
element-name*	Use once, many times, or not at all	<element (child1*, child2+, child3)>
( )	Indicates groups; may be nested	<element (#PCDATA | child)*> or <element ((child1*, child2+, child3)* | child4)>

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