Element declaration in DTD Specifies the name of the tag that use to build XML document. Every (General) XML element declare by following way,
<!ELEMENT element_name (inside_element)>
element_name specifies the general identifier and inside_element specifies what are content inside the element.
Elements with any Contents
Elements declared with the ANY keyword, Any keyword contain any combination of parse-able data.
<!ELEMENT element_name ANY> <!-- Syntax-->
<!ELEMENT div ANY> <!-- Example-->
EMPTY keyword specifies the empty tag. Inside no any element content.
Empty Element
<!ELEMENT element_name (EMPTY)> <!-- Syntax-->
<!ELEMENT br EMPTY> <!-- Example-->
EMPTY keyword specifies the empty tag. Inside no any element content.
Only Text Content Element
If your element content only text data you can declare.
<!ELEMENT element_name (#PCDATA)>
#PCDATA (parsed character data) keyword specifies parsed only character content.
Only One Child Element
If your element content only text data you can declare.
<!ELEMENT element_name (child_element)> <!-- Syntax-->
<!ELEMENT div (p)> <!-- Example-->
This declaration specifies
<div>...</div> only have one child <p>...</p> element.
Multiple Child Element
Child elements specifies one or more separated by comma (,) sign.
<!ELEMENT div (p,a,span,h3)> <!-- Example-->
Multiple Child Element (with same name)
Child elements specifies one or more time along with same name. add + sign end of the child element name.
<!ELEMENT div (p+)> <!-- Example-->
Occur any number of child element (* sign) :
Child elements specifies any number of deep child of child element. add * (asterisk) sign end of the child element name.
<!ELEMENT div (p*)> <!-- Example-->
Optional child element(? sign) :
Child element optional if not use in XML document, you can say element_name contain empty.
<!ELEMENT element_name (child_element?)> <!-- Syntax-->
<!ELEMENT div (p?)> <!-- Example-->
Mixed Operator :
You can use mixed operation with together.
<!ELEMENT div (p+,a*,span?,h3)> <!-- Example-->
OR (|) Operator :
You can also specifies the choice of multiple child element using pipe sign (|) operator.
<!ELEMENT element_name (child_element | child_element | child_element)> <!-- Syntax-->
Suppose following specifies the child elements separated by pipe sign. You can use any of the specified child element.
<!ELEMENT div (p | a | span | h3)> <!-- Example-->
Group Elements :
You can also specifies the group of element with specific operator.
<!ELEMENT article (header,(p,a,span,)*, footer)>
<!ELEMENT article (header,(p,a,span)+, footer)>
<!ELEMENT article (header,(p,a,span)?, footer)>
<!ELEMENT article ( header, ( p | a | span )*, footer ) >
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