Well, I was going to say "Collapse All By Level" did that, and then I tried it, and now I don't know what the heck "Collapse All By Level" does at all.
"Collapse All Completely" collapses all projects to the top level. That's exactly what I expected.
But given that, I expected "Collapse All By Level" to collapse all projects to the current level, i.e. the level the cursor is on. It doesn't do that. Not only doesn't it do that, it doesn't collapse all projects at all. Not only does it not collapse all projects, it seems to collapse a random project, as it's not the project the cursor is on. And, not only does it not collapse the cursor the cursor is on, it doesn't collapse to the level the cursor is on.
To use your example above, I positioned the cursor at the beginning of Project D: and selected Collapse All By Level. It collapsed the equivalent of B Task 1.2, if B Task 1.2 had sub-tasks and there was a B Task 1.3. IOW, not Project D:, not to the project level but two levels below, and a seemingly random project and level (not the project I was on, not the project prior to the project I was on, but a project two projects away, and then a random task at a random level beneath it.)
Jesse, what is it that "Collapse/Expand All by Level" is supposed to do? I've read the User's Guide paragraph four times, and it still doesn't make sense. Not only is the paragraph ambiguous (to me, anyway), but the behavior doesn't seem to have any correlation to the description at all.