The gist of if? Think of it as four values: a,b,c,d.
- a= count 1 if the declaration is from is a 'style' attribute rather than a rule with a selector, 0 otherwise (= a) (In HTML, values of an element's "style" attribute are style sheet rules. These rules have no selectors, so a=1, b=0, c=0, and d=0.)
- b= count the number of ID attributes in the selector (= b)
- c= count the number of other attributes and pseudo-classes in the selector (= c)
- d= count the number of element names and pseudo-elements in the selector (= d)