Omission test for XPs: Sentence fragments
Basis of test
Only phrases (hence constituents) like NP, AP, PP, VP can serve as answers to questions.
This is not surprising since question formation generally involves the use of a proform for the constituent which is then used to form the answer.
Test sentence: John will meet Sally at the train station.
Who will meet Sally at the train station? John. (NP)
Where will John meet Sally? At the train station. (PP)
Who will John meet at the train station? Sally. (NP)
What will John do? Meet Sally at the train station. (VP)
* Will meet Sally at the train station. (I') (For further information on INFL as a functional head click here.)