I was wondering if there were any "rules" regarding using pocket squares. For example, with respect to different square fabrics and patterns. (By this I mean questions like: is a silk pocket square more "casual" than a linen one, or vice versa? Is there any difference in the formality of a patterned vs. solid color square?) Also, is it considered acceptable to wear a square with no tie? Maybe there are no rules at all? Just curious.