That was the case in CSS 1.0, in 2.0 and later you can group classes in a single tag.
Match when the element's "att" attribute value is a space-separated list of "words", one of which is exactly "val". If this selector is used, the words in the value must not contain spaces (since they are separated by spaces).
Working with HTML, authors may use the period (.) notation as an alternative to the ~= notation when representing the class attribute. Thus, for HTML, div.value and div[class~=value] have the same meaning.This means that some browsers that don't understand newer CSS may have trouble with multiple classes in a single tag, but I don't know of any off the top of my head.