Yes indeed, the project I'm toying is a dungeon crawler and it would be restricted to viewing along the Z-axis with just a bit of glancing up/down. I've put together an image to illustrate the effect:

https://goo.gl/photos/ZeQvMN2HxZ9w9zrF6

In old pseudo-3D games such as Eye of the Beholder and Black Crypt this effect is quite pronounced. In Grimrock the effect is somewhat more subtle but the center of the red cross is some 60px above the center of the viewport. To the right you see what I've got right now and though I can tune down the pitch some one can still see that the vertical walls aren't parallell and it looks worse when it moves/animates. It also gets progressively worse as the architecture gets taller and/or thinner, I doubt pillars will look very nice. It's actually quite hard to get the tradeoffs right in situations such as wanting to see the floor when you're standing up close to a wall and similar.

There was another person working on a dungeon crawler and asking for the same things in this forum a couple of years ago and he was satisfied with your answer to raise and tilt the camera but I'm probably a bit more fussy. It bugs me because the tradeoffs are clearly noticeable once you understand them and the solution seems simple. But "seems" is always hard to nail down and I actually figured that this might mess up more of your calculations than you might care to change.

In any event I'm very happy with your library and most grateful for your hard work, thanks a whole bunch! 

But if I move the camera down I will be looking up at things I was previously level with. Imagine you have a frame (the viewport) in front of you and through it you can see an object at eye level. If I move my head up/down my perspective on the object will change as I will see it slightly from below. What I want to achieve and what those up/down parameters seem to do is to slide the frame downwards instead. That is what the up/down parameters seem to do if I've not misunderstood things horribly (which I'm admittedly prone to do). When I can only control the angle covered in the y-direction (and indirectly at that, which I am fine with) I am left in a situation where the vanishing point for lines which are parallel to the direction of my camera is always placed in the exact center of the screen, e.g. "up" and "down" are always equal. I want to shift that vanishing point up the screen.

Does that make more sense?