In an execution plan, the order of the lines is well defined, but not always easy to spot, especially for the untrained eye.
This idea is based on some discussions, and a good example can be seen in https://asktom.oracle.com/pls/apex/asktom.search?tag=confuse-at-the-order-of-execution-plan-table.
The xplan.display_cursor script can easily add a Order column, so this can not be a technical problem to implement. In best case, an additional format option +order can be provided.