foldexpr '<1' results in a level-3 fold

[lilydjwg]

Steps to reproduce

1. Edit the following file with vim --clean:

/
├── e
│   └── d
│       └── c
│           ├── _a
│           └── _b
└── f

x directories, y files

2. source the following vimscript:

let s:fold_results = [ '>1', '>2', '>3', '>4', '4', '<4', '<1', '0', '0' ]

function FoldExpr(lnum)
  return s:fold_results[a:lnum-1]
endfunction

set foldmethod=expr foldexpr=FoldExpr(v:lnum)

3. observe that line 7 is at level 3

Expected behaviour

<1 should end any higher-level folds and end at level 1.

Version of Vim

9.1.514

Environment

Arch Linux, GNOME Termianl / GTK GUI

Logs and stack traces

No response

[zzzyxwvut]

The following lists appear to correctly map fold levels for
the example file:

let s:fold_results = [ '>1', '>2', '>3', '>4', '4', '<2', '<1', '0', '0' ]
let s:fold_results = [ '>1', '>2', '>3', '>4', '4', 's3', '<1', '0', '0' ]
let s:fold_results = [ '1', '2', '3', '4', '=', '=', '1', '0', '0' ]

I guess, the outermost (shallowest) level is expected for
< when multiple folds end on the same line.

[lilydjwg]

Yes, after adjusting the < value it folds as expected. But the doc doesn't say so. So either this should be fixed, or the doc should be updated, shouldn't it?