Then go to the index_level column explanation:
The nonleaf levels of indexes are only processed when mode = DETAILED.
Now go to the Scanning Modes section:
The LIMITED mode is the fastest mode and scans the smallest number of pages. For an index, only the parent-level pages of the B-tree (that is, the pages above the leaf level) are scanned. For a heap, the associated PFS and IAM pages are examined and the data pages of a heap are scanned in LIMITED mode.
With LIMITED mode, compressed_page_count is NULL because the Database Engine only scans non-leaf pages of the B-tree and the IAM and PFS pages of the heap.
The scanning modes section is wrong, right? Limited mode only scans leaf pages. Let me know your thoughts. I wanted to check with the community before posting it to the proper channels.