ivaynberg/select2 — pull request #2203 by jesperronn (2014-03-23 20:57:21+00:00)
Title: Reduced 10 level deep nesting of CSS rules. Instead, using the simpler d...

...epth-0,-1,-2,etc for adding padding to the result when nested.

Greatly simplifies complexity of expressions and reduces (hopefully) rendering time.

From https://developers.google.com/speed/docs/best-practices/rendering#UseEfficientCSSSelectors
Descendant selectors are inefficient because, for each element that matches the key, the browser must also traverse up the DOM tree, evaluating every ancestor element until it finds a match or reaches the root element.