Sorry, I believe, the explanation in the file above is not correct. There’s no such thing as “combo class” in CSS, but there’s a selector of .classA.classB type pointing to an element that has ALL the classes listed in its description. In no particular order, maybe with another class listed between the entries.
P.S. There’s also a typo in the example B in “Global classes, Combo classes and Specificity” chapter. should be discreet instead of stand-out. Because of overwriting by selector’s declaration, the result text would look 10% and underlined (the latter goes for Example C as well).
And again, I believe, the explanation behind the example is not correct. it’s not a matter of “priority”. It’s a matter of finding both classes in an element. When a browser finds such an element, it applies the properties of .classA to it, then the properties of .classB, and finally the properties declared for the selector .classA.classB itself.
I think, this is not a very intuitive concept, but it seems this is how it works.