replacing the default features with {HEAD ~ the modifications} to form {TAIL ~ a set} of customized features 
to form
replacing the default features with { HEAD ~ the modifications } to form { TAIL ~ a set } of customized features
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH