Looking for example of BOOST_CLASS_REQUIREx

I'm trying to find an example of how to invoke the BOOST_CLASS_REQUIREx macro (from the concept_check library). Can anyone point me in the right direction? Thanks, --Steve Stephen Gross Case Western School of Medicine Cleveland, OH "By Grabthar's hammer, by the sons of Worvan, you shall be avenged." - Dr. Lazarus