Just noticed that there are apparently two 'file display border' entries in the helpfile, one is shown as 'File Display border' (lowercase "b" on "border") and the other as 'File Display Border' (uppercase "B" on "Border").
There are two different pages, one about the File Display Border itself. The other about the File Display Border page in Preferences.
The same is true for several other titles (e.g. Filter Bar).
It's just an artifact of the Windows Help viewer not showing enough context about where the pages are in the table of contents, if you use the Index or Search tabs instead of the Contents tab.