move mode for stacks of blocks

[maribethb]

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Problem

there is no way to move multiple blocks with keyboard but there is with mouse

Request

add a shortcut for moving the current block + its children (the same group of blocks that would be moved if you start a mouse move)

personally I think that the default M should match what the mouse does and move the whole stack, and option+M or whatever should move a single block (matches option+click and drag to move a single block) BUT the rest of the team thinks the mouse behavior is wrong, and we should add multi-select, and then change the mouse behavior so that it only moves one block by default unless you've multiselected something, and therefore move mode should just continue moving one block but option+M (or whatever) should move the stack. so let's do that for now barring feedback otherwise.

Alternatives considered

No response

Additional context

No response

[cpcallen]

In the short term we (@rachel-fenichel, @gonfunko and @cpcallen) agree that we should add a way (probably modifier) to allow the keyboard to move stack (i.e. disable stack heal on move start).

We don't want to change the keyboard behaviour to match the mouse because we think it would be better long term to change the mouse behaviour to match the current keyboard behaviour. (We were thinking that we would do so as part of implementing multiselect, but we could make the change sooner just by inverting the meaning of the existing alt/option modifier when dragging. That does not obviate the problem with changing a long-standing behaviour that will doubtless affect many published educational materials.)