... Authors can provide guidance as to the relative widths of columns, but user agents should ensure that columns are wide enough to render the width of the largest element of the cell's content. ... The default table width is the space between the current left and right margins, but may be overridden by the width attribute on the TABLE element, or determined from absolute column widths. ... If the table width is specified with the width attribute, the user agent attempts to set column widths to match. ...