Reorder and merge/unmerge list of items

I have a list that consists of blocks of one or more items. For example, there are 3 blocks with a total of 5 items in the following image.

list

The user can add items, decide what items are grouped in a block, the order of the blocks and items within the blocks. There is usually only 1 item per block, and almost always 4 or less. There are usually 30-100 blocks.

What are the best user controls to provide?

My idea is that the user can perform the following actions:

  • Reorder blocks (and all the items in it)
  • Move/reorder items into blocks
  • Move/reorder items out of blocks

But I can't think of suitable controls, other than left-click-drag-drop and right-click-drag-drop, which aren't enough for the actions.

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