A tree summary view which displays only the second dimension, only when/now steps (but also "hidden" ones, see ticket #28) and their secondary ancestors.
when/now steps that are "hidden" should on clicking select the lowest non-hidden ancestor in the main tree view.
Offer a possibility to find out easily which when step corresponds to which now step.
Offer the user the option to hide when steps and corresponding now steps that are still in the future in the currently selected step.
Offer the user the option to hide when steps (and corresponding now steps) if there is a completed corresponding now step in the current primary branch.
Offer the user the option to hide when steps and corresponding now steps if all of these steps are "hidden".