Intertextuality: There are clearly noted connections between Scriptures ("it is written"), as well as many allusions, etc. to the Scriptures. The OT is clearly referenced often within itself and by the NT, but fewer clear connections of NT to NT (though not absent).
I hold to the priority of Matthew, and reject the theoretical (fictional in my mind) Q document, largely because if one believes the divine side of inspiration, no literary connection is even needed between the Gospels, as the Divine mind can guide to different witnesses to write the same thing (that does not mean a source as not used, but it is irrelevant and a waste of time to speculate on).