AT Scope 1 commits or rolls back Tx1.1, then ends MTx resumes.
MTx invokes AT Scope 2. MT suspends, passing control to AT Scope 2, which initially is performing queries.
AT Scope 2 then begins Tx2.1 by, say, doing an update. AT Scope 2 commits or rolls back Tx2.1.
Later, AT Scope 2 begins a second transaction, Tx2.2, then commits or rolls it back.
AT Scope 2 performs a few queries, then ends, passing control back to MTx.
MTx invokes AT Scope 3. MTx suspends, AT Scope 3 begins.
AT Scope 3 begins Tx3.1, which in turn, invokes AT Scope 4. Tx3.1 suspends, AT Scope 4 begins.
AT Scope 4 begins Tx4.1, commits or rolls it back, then ends. AT Scope 3 resumes.
AT Scope 3 commits or rolls back Tx3.1, then ends. MTx resumes.
Finally, MT Scope commits or rolls back MTx, then ends.