Twenty-five rules and two buttons that move one place at a time meant a
rule pushed to the wrong end cost ten clicks to bring back. It can now
be dragged.
A grip on the left of each card arms the drag, so the switch, the name
and the buttons still take a plain click, and the up and down buttons
stay for the keyboard. The card being dragged fades; the one under the
pointer draws a line on the edge the rule would land on, top half or
bottom.
The guard against dropping a rule onto itself reads a ref rather than
state: dragstart and the first dragover can arrive in the same frame,
and a stale read there drew a drop line on the card being dragged. Found
by driving the real thing in a browser, and covered by a test that fires
the two events back to back.
jcoffey-dev
4740ca46eb