Attributes are given in the opening tag of an element and have a name and a value pair. The name part of attribute is actually a property of the element and value gives a value (whether text or number) for that property like, ‘xmlns’ attribute describes the XML namespace for the XHTML document to refer to and to specify XHTML 1.0 namespace a value of “http://www.w3.org/1999/xhtml” is given.
Attributes are divided into three groups which are
Core attributes: It consist of class, id and title attributes
Internationalization attributes: It consist of dir, lang and xml:lang attributes
UI event attributes: They are linked to events like onclick, ondoubleclick, onmousedown, onmouseup, onmouseover, onmousemove, onmouseout, onkeypress, onkeydown onkeyup
Core and internationalization attributes together are also called universal attributes.