CSS: Use tag type before ID?

Question

One of the guys here at work puts the tag name in front of all his CSS selectors for element ids. For example:

div#footer {

}

This, as opposed to just:

#footer {

}

His rationale is that this is a quicker lookup for most browsers because they don't need to check the id attributes of every type of element--just div elements. He also points out that this should be done with classes (e.g. div.header-label for <div class="header-label"... elements).

Sounds reasonable and rational, but is it true?

Answer 1

Your co-worker is wrong, it's exactly the opposite:

• https://developer.mozilla.org/en/Writing_Efficient_CSS
• http://code.google.com/intl/de-DE/speed/page-speed/docs/rendering.html

But also have in mind that CSS optimization is micro-optimization and finally just irrelevant in most cases:

• http://meiert.com/en/blog/20090312/performance-of-css-selectors/