The WorldWideWebConsortium standards for representation of documents (for instance, HtmlDocuments with CascadingStyleSheets and ExtensibleMarkupLanguage documents) as an object model. Three levels of the specification exist, where each is a superset of the last, and levels 2 and 3 are separated into modules. See http://www.w3.org/DOM/ for details. Level 1 and most of level 2 are supported by major web browsers for Javascript (the primary audience).

Often mistakenly thought to be part of JavaScript, as that language is most commonly used to manipulate the DocumentObjectModel and its predecessors. --NickFitzsimons

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''The group news:comp.lang.javascript is always ready to cheerfully and helpfully field questions about HTML and DOM.''

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The DocumentObjectModel is also used to represent the parse trees for XML (ExtensibleMarkupLanguage) documents. -- EdwardKiser
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CategoryXml {EditHint: why this category, may I ask} ''It links a collection of pages related in some way or another to XML.''