A few interesting quotes about performance optimization from the article:
"Firefox blocks all scripts when there is a style sheet that is still being loaded and parsed. Webkit blocks scripts only when they try to access certain style properties that may be affected by unloaded style sheets."
"WebCore simply throws a global switch when any sibling selector is encountered and disables style sharing [optimization] for the entire document when they are present. This includes the + selector and selectors like :first-child and :last-child."
"After parsing the style sheet, the rules are added to one of several hash maps, according to the selector. There are maps by id, by class name, by tag name and a general map for anything that doesn't fit into those categories." Every element then looks in these maps to find rules which might apply to it.
"Firefox blocks all scripts when there is a style sheet that is still being loaded and parsed. Webkit blocks scripts only when they try to access certain style properties that may be affected by unloaded style sheets."
"WebCore simply throws a global switch when any sibling selector is encountered and disables style sharing [optimization] for the entire document when they are present. This includes the + selector and selectors like :first-child and :last-child."
"After parsing the style sheet, the rules are added to one of several hash maps, according to the selector. There are maps by id, by class name, by tag name and a general map for anything that doesn't fit into those categories." Every element then looks in these maps to find rules which might apply to it.