{HEAD ~ R4} is {TAIL ~ halogen}, alkoxy, phenylthio or phenoxy, which may be substituted or unsubstituted 
is
{ HEAD ~ R4 } is { TAIL ~ halogen } , alkoxy , phenylthio or phenoxy , which may be substituted or unsubstituted
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH