Spec says

"for $b score $s 
    in /books/book[content ftcontains "web site" && "usability" 
                   and .//chapter/title ftcontains "testing"]
return $s"

Since ftcontains returns boolean and score, how does it combine score since it only operates on boolean. We need to make the processing clearer (2nd order operation applyscore(( E ))). E.g.:
for $i in score $s in Expr where return  => for $i in Expr let $s := applyscore(( Expr[$i] )) where  return