The basic one is to separate content from presentation. In the above table examples, we have the classic challenge of defining cleanly the boundary between structure and format. Obviously, a matrix of data is a useful structure. Clear distinctions are not created by syntax, but by designers who create an intelligible partition between media, structure, and appearance. A validator that checks syntax to see what you site does in several browser environments including Lynx.
Syntax checkers are often more concerned with minor variations of syntax that browsers are.
That is, a page may do well, but have many non-standard features disregarded by browsers. Lynx is quite good at bypassing superfluous parameters. A complete evaluation of a complex site is subtle. Full access is the result of a deep desire to make what you create available to all, a sensibility of inclusion. And, some hard thought about which techniques to use.