{HEAD ~ Z3} represents {TAIL ~ the atoms} necessary to complete a mono or bicyclic aromatic or heterocyclic ting system containing 5 to 10 ring atoms and C is in an ortho or para position relative to W 
represents
{ HEAD ~ Z3 } represents { TAIL ~ the atoms } necessary to complete a mono or bicyclic aromatic or heterocyclic ting system containing 5 to 10 ring atoms and C is in an ortho or para position relative to W
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH