For 1: Yeah, I agree that for bullet clicks the current behaviour is best (click should open in same panel, SHIFT in the other). What I’m suggesting is an alternative behaviour for the situations in which it’s not clear (from search and from sidebar).
For 2: Lot’s of variables to consider here… Here’s an initial suggestion:
One panel would always need to be set as the “Primary” one. By default, its the one on the left (so if a user doesn’t want to bother with that, its always clear which is primary).
Then:
When opening a reference from Search or sidebar
Click: opens on primary document
CTRL+SHIFT+click: open in a new panel
SHIFT+click: if there’s only one panel, behave same as CTRL+SHIFT+click; if two, open in the non-primary panel
When opening from clicking on a bullet
Click: open in same panel
CTRL+SHIFT+click: opens in a new panel
SHIFT+click: if one panel, same as above; if two, open in the other panel.
Regardless of the situation, if there are more than two panels, maybe open in the one most recently interacted with? (alternatively, allow defining a Secondary panel. But that might be too messy)
The shortcuts for creating/opening documents can have similar variations. For example, creating a new document would be ALT+D (opens on primary document), ALT+CTRL+SHIFT+D (new panel) and ALT+SHIFT+D (the other). (could be clumsy)
Would be good to allow users to customize some of the above. At least to flip click with SHIFT+click.
Nice-to-have: be able to just drag a reference into an existing panel to open it there (or in-between them to insert a new one).