I did not want a second ordering system sitting next to WordPress. The number you drag is menu_order on the post, the column that has been there the whole time. Pages have shown it as Order for years. Posts have the same column, and almost nothing in core sorts posts by it.
What a drop writes
You drop a row. The plugin saves that post’s menu order and, if the type is hierarchical, its parent. Then it walks the siblings under that parent and rewrites their menu order so the list is 0, 1, 2, and so on, in the order you see. It does this in batches, which is why a long list takes a breath after a drop.
The reorder screen itself always reads that list ascending, menu order first and title as the tiebreaker. Low number at the top. The public site does not read it until a query asks. See Why the admin order and the public order can differ.
What is not stored
- No custom table. Uninstalling deletes the plugin’s settings option and leaves every post’s menu order where it was
- Deactivating does not clear those numbers either. Turn the plugin back on and the order is still there
- The screen only loads published posts. A draft keeps whatever menu order it already had, and you cannot drag it here
- Order inside a category is not this column. A post has one menu order, not one per term
That single number is the whole design. Any query in WordPress can sort by it, which is also why a query that never mentions it will ignore your drag completely.