how to test text to see if maybe it is UTF-8????

From: lawrence (lkrubner_at_geocities.com)
Date: 09/29/04 

Date: 29 Sep 2004 14:44:25 -0700

Someone on www.php.net suggested using a seems_utf8() method to test
text for UTF-8 character encoding but didn't specify how to write such
a method. Can anyone suggest a test that might work? Something that
maybe gives 90% confidence that a given block of text is or is not
UTF-8 encoded?