DnD: introduce selfCopy flag

[Eugene Lazutkin]

Presently there is copyOnly flag, which forces items to be copied always. Users (including Revin Guillen) ask for more complex behavior: copy should be forced only when source != target. For self-drops it should be able to move (rearrange) items by default.

In order to to accomplish that we will introduce selfCopy flag:

• When true, all self-drops copy items like the current behavior.
• When false, all self-drops move/rearrange items. This behavior can be overridden by keyboard (by pressing Ctrl or Meta key).

By default this flag is false.

[dante]

another thing to think of: it seems terribly difficult to prevent a copyOnly="true" from being able to self-populate (copy and drop into own source). A common use case is to drag from a source to a target but prevent self-dropping. Revin has a workaround in his blog post, but it seems like it would be a trivial thing to introduce into DnD natively. sourceOnly or something?

this is not a full feature request, just something to consider.

[Eugene Lazutkin]

(In [14152]) DnD: adding selfCopy flag. Thx, Revin Guillen! Fixes #7051. !strict

[Eugene Lazutkin]

(In [14158]) DnD: adding selfAccept for copyOnly sources, thx, Revin Guillen! Refs #7051. !strict