2008 Oct 17
The regular expression repetition notation {1,4} used in CSS has a fixed meaning in terms of which edge each case refers to. It is clockwise from the top.
Thus a sequence of four value expressions are implicitly: top right bottom left.
When there are fewer than four the rules are:
(3) left missing - use right for left
(2) repeat pair: use top for bottom ,
and use right for left
(1) all four use same value.