CSS

====Pseudo-classes====
''Pseudo-classes'' are used in CSS selectors to permit formatting based on information that is not contained in the document tree. 

One example of a widely used pseudo-class is {{code|lang=css|:hover}}, which identifies content only when the user "points to" the visible element, usually by holding the mouse cursor over it. It is appended to a selector as in {{code|lang=css|code=a:hover}} or {{code|lang=css|code=#elementid:hover}}. 

A pseudo-class classifies document elements, such as {{code|lang=css|code=:link}} or {{code|lang=css|code=:visited}}, whereas a ''pseudo-element'' makes a selection that may consist of partial elements, such as {{code|lang=css|code=::first-line}} or {{code|lang=css|code=::first-letter}}.<ref>{{cite web |url=https://www.w3.org/TR/CSS21/selector.html#pseudo-elements |title=W3C CSS2.1 specification for pseudo-elements and pseudo-classes |publisher=World Wide Web Consortium |date=7 June 2011 |access-date=30 April 2012 |archive-url=https://web.archive.org/web/20120430011514/https://www.w3.org/TR/CSS21/selector.html#pseudo-elements |archive-date=30 April 2012 |url-status=live }}</ref> Note the distinction between the double-colon notation used for pseudo-elements and the single-colon notation used for pseudo-classes.