The NCAA’s guide to how the 68 teams are chosen, seeded and bracketed for the Division I men's basketball tournament every season.
www.ncaa.com
Each region is divided into quadrants with four levels in each, permitting the evaluation of four different sections within each region against the same sections in each of the other regions.
The committee will assign all four teams in each bracket group (seeds 1, 16, 8, 9), (4, 13, 5, 12), (2, 15, 7, 10), (3, 14, 6, 11) to the same first-/second-round site. There will be two ”pods‟ at each first-/second-round site which may feed into different regional sites.
Each of the first four teams selected from a conference shall be placed in different regions if they are seeded on the first four lines.
Teams from the same conference shall not meet prior to the regional final if they played each other three or more times during the regular season and conference tournament.
Teams from the same conference shall not meet prior to the regional semifinals if they played each other twice during the regular season and conference tournament.
Teams from the same conference may play each other as early as the second round if they played no more than once during the regular season and conference tournament.
Any principle can be relaxed if two or more teams from the same conference are among the last four at-large seeded teams participating in the First Four.
To recognize the demonstrated quality of such teams,
the committee shall not place teams seeded on the first four lines at a potential “home-crowd disadvantage” in the first round.
That's the full context of the rule. As gonzalo said, this would seem to make East Region as a two seed impossible (if Duke is seeded there).