6. Unnecessary Use of Proprietary Attributes
Back in the days before CSS became so available to us, we had to rely on lots of browser-based, proprietary elements and attributes to create visual output. One such example is the use of proprietary margin properties in the body element:
<body leftmargin="10" topmargin="0">
But CSS has come to the rescue, and in almost all cases in contemporary web design, we can rely on CSS to achieve the results we're after. On the few occasions when a consistent look is required for older browsers there may be a need to fall back on such proprietary attributes, but it's rare. Even if you had to accommodate such a situation, you could do so by using a very streamlined table for layout along with CSS and reduce the use of these attributes, or (better yet) remove them altogether.