The other day I was writing some updates and improvements for Modernizr, one to detect for generated content support and two to improve stylesheet and element injection. Modernizr already in a few places inserts a stylesheet and a corresponding element to do some tests e.g. Continue reading.
css3transforms and a few others. All this happened multiple times; each test would inject an element and an inline style element, do its test then remove both elements. All this happens while the page is loading and as you can see the more tests that involve these steps exponentially grow the number of times it needs to touch the DOM.