What does ‘Group Repeats Hierarchically’ mean?

This option is used when the group represents a hierarchical structure that can contain an unknown number of levels. For example, the SQL for a repeating level would be:

This kind of query could give an unlimited number of levels in a hierarchy, so the parameter for ‘PARENT_NODE_ID’ is either {NODE_ID} (i.e. the ID of the node clicked on), or 0 if we’re at the top level.