DTD Symbols

The following is a list of symbols used in a DTD content model. The content model identifies the child elements that can appear in a parent element, the order in which they appear and the frequency in which they appear.

Symbol	Description	Example
\|	Either element must appear. (Element A or element B must appear)	`<!ELEMENT BOB (A \| B)>`
,	Requires the elements to appear in the listed order. (Element A must appear followed by element B)	`<!ELEMENT BOB (A, B)>`
?	Element is optional. If the element is used, it can only appear once. (Element A may appear once or not at all)	`<!ELEMENT BOB (A?)>`
*	Element may appear zero or more times. (Element A may appear zero or more times)	`<!ELEMENT BOB (A*)>`
+	Element must appear at least once. It may also appear multiple times. (Element A must appear at least one or more times)	`<!ELEMENT BOB (A+)>`
( )	Groups nested elements.	`<!ELEMENT BOB ((A, B) \| C)>`
no symbol	One and only one element must appear. (Element A must appear only one time)	`<!ELEMENT BOB (A)>`