please explain Euro 2016 regulation

here are the official Euro 2016 regulations.(PDF)

Please explain to me Article 18.01

a.
higher number of points obtained in the** matches played among the teams in
question;**

d. if, after having applied criteria a) to c), teams still have an equal ranking,
criteria a) to c) are reapplied exclusively to the matches between the teams in
question to determine their final ranking

What is the difference?
Thanks.

Imagine 3 teams X, Y and Z are tied on points. If criteria a) to c) are applied to games between X, Y and Z and X is determined to have finished higher (or lower) than teams Y and Z, but teams Y and Z are still tied, then criteria is reapplied to games between Y and Z to determine the placings of teams Y and Z.

I’ll re-read it and try again.