Finds positions of all subsets matching a pattern.
SubsetPosition[list, sublist]
SubsetPosition[list, patt]
SubsetPosition[list, patt, n]
SubsetPosition[{1, 2, 3, 4, 5}, {_, _}]
→ {{1, 2}, {1, 3}, {1, 4}, {1, 5}, {2, 3}, {2, 4}, {2, 5}, {3, 4}, {3, 5}, {4, 5}}