Originally Posted by dgatwood
With the caveat that this has lower specificity. That usually
doesn't matter (a class by itself is supposed to have higher specificity than any number of leading elements even if some of them have a class). However, not all readers follow the specificity rules correctly, and I've actually seen situations where ADE violates that rule, so be sure to test your content in a wide range of readers before you do anything that would reduce specificity of a CSS selector.
I prefer not to stick classes to anything. They are better free form. So p.hd would be just .hd. It works in all cases where CSS is respected. So no need to test .hd as the class in the CSS. Any reading software that breaks if it is just .hd is too buggy to even bother with. ADE does work with .hd so no problem there.