files/en-us/glossary/attribute/index.md
An attribute extends an {{Glossary("HTML")}} or {{Glossary("XML")}} {{Glossary("element")}}, changing its behavior or providing metadata.
An attribute always has the form name="value" (the attribute's identifier followed by its associated value). You may see attributes without an equals sign or a value. That is a shorthand for providing the empty string in HTML. However, this is not valid in XML: XML requires all attributes to have an explicit value.
A number of HTML attributes are {{Glossary("Boolean/HTML", "boolean attributes")}}. These attributes' values are only controlled by the presence or absence of the attribute. See {{Glossary("Boolean/HTML", "boolean attributes")}} for more information.
Attributes may be reflected into a particular property of the specific interface.
This means that the value of the attribute can be read or written directly in JavaScript through a property on the corresponding interface, and vice versa. The reflected properties offer a more natural programming approach than getting and setting attributes using the {{domxref("Element.getAttribute()","getAttribute()")}} and {{domxref("Element.setAttribute()","setAttribute()")}} methods of the {{domxref("Element")}} interface.
For more information see Attribute reflection.