2.1.21 [CSS-Level2-2009] Section 6.4.4, Precedence of non-CSS presentational hints
The UA may choose to honor presentational attributes in an HTML source document. If so, these attributes are translated to the corresponding CSS rules with specificity equal to 0, and are treated as if they were inserted at the start of the author style sheet. They may therefore be overridden by subsequent style sheet rules. In a transition phase, this policy will make it easier for stylistic attributes to coexist with style sheets.
Quirks Mode and IE7 Mode (All Versions)
The cellspacing, frame, rules, framebar, hspace, and vspace attributes are not overridden by subsequent style sheet rules.
IE8 Mode and IE9 Mode (All Versions)
The noshade attribute is not overridden by subsequent style sheet rules.