where MSC is a single MSC entry like 16-XX, 16Kxx, 16K50
A two digit MSC entry like 16 is allowed and automatically extended to 16-XX.
It inserts appropriate category entries for the MSC entry into the page from which it is called, thereby categorizing this page, unless it is called from a category file, in which case it does nothing.
Category. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Category&oldid=35347