Where/how is "custom" sorting customized?

[zarlan]

Under "sort by", there is the option of "custom".
It's clearly not anywhere in settings, so…
Where/how is it customized?

[XnTriq]

Please take a look at Tools → Settings… → File list → Custom filter.

[zarlan]

The settings for the custom filter, where you decide what items to show, when you choose "custom" in "Filter by", has no possible relevance for the custom manner of sorting, when choosing "custom", under "Sort by".
It has options of what file types/formats to be visible, shown as thumbnail, and shown in preview.
None of those options, have even the faintest hint, of relevance or applicability, to sorting.

So can you please explain to me, what possible reason you have, for directing me there?

[XnTriq]

The settings for the custom filter, where you decide what items to show, when you choose "custom" in "Filter by", has no possible relevance for the custom manner of sorting, when choosing "custom", under "Sort by".
It has options of what file types/formats to be visible, shown as thumbnail, and shown in preview.
None of those options, have even the faintest hint, of relevance or applicability, to sorting.

So can you please explain to me, what possible reason you have, for directing me there?

Users can re-arrange files in browse mode via drag-&-drop. MP will remember the customized sort order by placing a small hidden text file (.XnViewSort) into folders with manually rearranged images.

[zarlan]

Users can re-arrange files in browse mode via drag-&-drop. MP will remember the customized sort order by placing a small hidden text file (.XnViewSort) into folders with manually rearranged images.

That would appear to answer my initial question, which is appreciated, but it doesn't answer the question in the comment you replied to:
Can you please explain to me, what possible reason you had, for directing me to Tools → Settings… → File list → Custom filter?