Changes in HTML 5 - <th> Tag
What's new in HTML 5
Differences between HTML 5 and earlier versions of HTML
The following attributes should not be coded on the <th> tag because they either have been deprecated or were never officially supported:
abbr
align
axis
bgcolor
char
charoff
height
nowrap
scope
valign
width
The 2000-2010 Recommendations from the W3C HTML Working Group defined the HTML namespace for the th element type name along with the names of all HTML element types. In older (pre-2000) versions of HTML, element type names were not associated with a namespace.