function Specificity(a, b, c, d){
    this.a = a;
    this.b = b;
    this.c = c;
    this.d = d;
}
Represents a selector's specificity.
@namespace parserlib.css
@class Specificity
@constructor
@param {int} a Should be 1 for inline styles, zero for stylesheet styles
@param {int} b Number of ID selectors
@param {int} c Number of classes and pseudo classes
@param {int} d Number of element names and pseudo elements