Changes in HTML 5 - <output> Tag
What's new in HTML 5
The <output> tag is one of the new elements in HTML 5.
Differences between HTML 5 and earlier versions of HTML
The <output> tag did not exist in older versions of HTML.
The 2000-2010 Recommendations from the W3C HTML Working Group defined the HTML namespace for the names of all HTML element types, which now includes the output element name. In older (pre-2000) versions of HTML, element type names were not associated with a namespace.