HTML element: Difference between revisions

Revision as of 23:37, 23 October 2004

Revision as of 03:48, 24 October 2004

Line 1:

In [[computing]], an '''HTML element''' (instance) in terms of [[SGML]] is the complete sequence of a start ''tag'' (with [[attribute]]s and their [[attribute value|value]]s), any embedded HTML content, and the end tag. A special case is [[empty element]]s that don't have contents and end tags. Due to the constraints of the [[Document Type Definition|DTD]]s, various parts, including start and end tag, may be omitted in [[HTML]], but not [[XHTML]]. In XHTML the minimized tag syntax for an empty element (abbreviated form of the combination of opening and closing tag) is e.g. <ttcode>&lt;br /></ttcode>.

Informally, HTML elements or their attributes are often simply called "tags" (an example of [[synecdoche]]), though many prefer the term ''tag'' strictly in reference to the semantic structures delimiting the start and end of an element.

Line 5:

=="Nesting"==

Most but not all HTML elements can be "nested": <code>&lt;p>&lt;em>You&lt;/em>rock!&lt;/p></code> has an <code>em</code> element nested inside a <code>p</code> element. This can become more complex, for example <code>&lt;h1>Children that &lt;em>do &lt;font color="red">not&lt;/font> clean up&lt;/em> their rooms&lt;/h1></code>. Nesting may be arbitrarily deep. Tags must be closed in the reverse order that they've been opened.

Tags must be closed in the reverse order that they've been opened. A so-called 'block-level' element cannot be nested inside an inline element.

;Wrong:

Line 13 ⟶ 11:

;Right:

:<code>&lt;p>&lt;font face="Tahoma">Lucy kissed &lt;em>Jimmy&lt;/em>&lt;/font>&lt;/p></code>

Nesting is restricted partly on the basis of whether an element is ''block-level'' or ''inline''. A block-level element typically begins on a new line, while an inline element typically does not; a block-level element may contain other block-level elements or inline elements, while an inline element may only contain other inline elements. Examples of block-level elements include paragraphs, lists, tables, headings, and the <code>div</code> generic container element. Examples of inline elements include include structured text such as emphasis, citations, or abbreviations, as well the <code>span</code> generic container element.

==Header tags==