Highlight current selection

[dethe]

We should put a CSS outline around selections or otherwise mark them (outline won't follow the shape of blocks well). Users can interact with selections in several ways:

There should almost always be 2 selected things: 1 step, context, or contains, and 1 value that is block-droppable. Exceptions are if there are no valid targets for the selection, or if the user intentionally multi-selects several blocks for another operation (cut/copy).

Selection after adding a block

1. Adding a step makes the step selected
2. Adding a context makes the context's wb-contains block selected
3. Adding an expression makes the first empty value of the expression selected, if any
4. Selecting a step or context also selects its first empty value.

Click blocks in script workspace to change selection

• Clicking on a block in the script workspace selects the block as if it were just added.
• Ctrl-click or Cmd-click will select a block without unselecting the previous block.
• Shift-click or drag should select contiguous blocks. [deferred, "contiguous" is tricky]
• Selecting a block should select the values of the block as if it were just added.

Click blocks in block menu to add block to script at selection

• Clicking on a block in the block menu should ATTEMPT to insert the block into the selection.

Clicking on a step or context:

• If contains is selected: insert into contains as first block (prepend)
• If a step or context is selected: insert after that block as a sibling

Clicking on an expression:

• If the selected value has a matching type, insert there
• If the selected value has a sibling with and open value and matching type, insert there
• Do not auto-insert into another block than the one with selected value.

Clicking on a block in a :

• Only add the block if it is in scope in the insert location
• If the user has multiple blocks selected, the first valid block in the selection should be treated as the selected block.
• If a block cannot be placed when clicked, the user should be informed why using the message view.

In all cases, once a block is added by clicking a block in the block menu, the new selection is the same as described above in "Selection after adding a block".