Move blocks between blocks fields

[mattddean]

As it stands, blocks can be drag-and-dropped within a container that accepts the block.

But sometimes you have multiple "blocks fields" on a page that accept the same block. Maybe you want to move a block from one of those containers to another.

Currently you have to rebuild the block in the other container. For simple blocks, this is fine, but sometimes you have a complicated block that takes time to recreate. It would be incredible if you could drag a block directly from one container to another.