Version //IETF//DTD HTML 2.0 Strict//EN
Content Notation

The allowable content of the elements is shown using a content model syntax.

NotationMeaning
( ) ( and ) are grouping symbols around elements and/or other symbols
A | B Either A or B occurs, but not both.
A , B Both A and B occur, in that order.
A & B Both A and B occur, in any order.
A? A occurs zero or one time.
A* A occurs zero or more times.
A+ A occurs one or more times.
-A A is prohibited at this point.
+A A could appear multiple times at various positions.
EMPTY this means that there must be nothing in the content;
elements with EMPTY content are called empty elements.

Examples from HTML 2

HTML Content

The allowable content of the HTML element is:

( HEAD, BODY )
This means that an HTML element must contain exactly one HEAD followed by exactly one BODY, in that order.

BODY Content

The allowable content of the BODY element is:

( H1 | H2 | H3 | H4 | H5 | H6 | P | UL | OL | DIR | MENU | DL | PRE | BLOCKQUOTE | FORM | ISINDEX | HR | ADDRESS | IMG )*
This means that all those elements shown could be content of a BODY element. Don't misinterpret the | symbol here--it does not mean that you can have to choose between having a H1 or a H4 in the same BODY. The notation means you can choose one of the elements within the ( and ). But the * at the end means you can repeat this choice as often as you wish. So you can have a H1, H2, or H5 in the same BODY.

HEAD Content

The allowable content of the HEAD element is:

( TITLE & ISINDEX? & BASE? ) +( META | LINK )
This means that a HEAD element can contain two groupings of possible elements. The first grouping consists of a TITLE element, an optional single ISINDEX, and an optional single BASE element. These can occur in any order. In the second grouping, META or LINK could appear multiple times at various positions within HEAD.
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