3.1.1 Rewrite rules and some terminology
On the top floor we have the phrase, XP. This is the highest level projected from the head and hence it is called the maximal projection. Another way of representing the maximal projection is X'', an X with two bars (pronounced ‘X double bar’), with the bars again representing the projection level. It seems that all phrases project to two levels and so we will not entertain the possibility of X''', or X'''', etc. Typically we will maintain the custom of representing the maximal projection as XP.