Question

Is there a performance difference between these 2 selectors assuming they match the same # of elements (a single form)?

#master .body form {}

#master form {}

I’ve heard that CSS selectors can make an appreciable speed difference for page rendering. I was also curious if this applies mostly to page load times or also for scenarios where you add a class to an element via JavaScript and how fast the browser can render that visual change.

Answer 1

interesting stuff in there:
http://calendar.perfplanet.com/2011/css-selector-performance-has-changed-for-the-better/, http://www.stevesouders.com/blog/2009/03/10/performance-impact-of-css-selectors/