It's more or less defined in 12.L.1a and b. If a position is overstaffed and the company decides to displace they must notify the affected pilots at least 14 days prior to the the effective date. There may or may not be any vacancies posted. The displaced pilots can bid their preferences for any position their seniority can hold. If they bump others out the process continues. Bump and flush. The CBA makes mention that all pilots (not just those displaced) should update their preferences in case they get bumped.