AVL Material Type Code.  LF, LF-Date, LF-Mark, LF-P/N, RoHS, RoHS-Date, RoHS-Mark, RoHS-P/N, and Unk are the AVL Material types that are hard-coded into the system. 

LF (Lead-Free), RoHS (the restriction of the use of certain hazardous substances in electrical and electronic equipment) or  (In general, RoHS requirements include limitations on other heavy metals in addition to being lead free. But many companies may not meet the full requirements of RoHS, but still want to identify the material as Lead Free(,  and Unk (Unknown) are the Inventory Material Types that are hard-coded into the system.  Then sometimes the user wishes to identify a date code, marking or part number which designates that the part has switched from unknown to LF or RoHS, and that is what the additional modifier is for.