Selecting a rectangular area in the code editor while holding the Alt key used to select a rectangular area and used to add one caret per row.
Now it still selects the rectangular area and adds one caret per row, but it also keeps the current caret.
Here the caret was after the set before I selected a rectangular area, and after the selection I have 3 carets:
Then, after typing XXX, I get the new text 3 times instead of two:
good point - moved to bug reports
we’ve added support for multiple cursors and the implementations are colliding.
we’ll adjust the keymap so that alt + shift will do rectangular selection
and alt (without shift) will do multiple cursors/selection
(This is the same behaviour as vscode)
This should now be fixed as above 
Now you can select a few expressions with Alt+mouse drags, then press ( and get all the expressions wrapped in (...).
One operation with the mouse to select them all, one click on the keyboard to wrap them all.
This is awesome, it might even save me almost half the time it takes me to write this!
Feeling good!