How to create block types that don't fill the whole voxel cube?

I'd like to have block types whose geometry only takes up part of a voxel - like the glass panes, slabs, and stairs in Minecraft.

1. Is that currently possible? Do I need a special module? If so, which one?

That's my main question, but here are some bonus questions if you're feeling generous:

1. If the answer to 1 is "yes": will my in-game avatar collide with the visible edges of the block, or with the edge of the voxel? For example, if I create a wall of glass panes, will I be able to move partway into that voxel (until I hit the actual glass), or will I hit an invisible wall (the edge of the voxel) just in front of the glass?
2. If the answer to 2 is "you won't collide with the edge of the voxel": will the player movement routines handle these blocks in a sensible way? For example, if I create a ramp or stair block type, and I run straight into one, will I climb it?

Basically, I'd like to create a game world that allows you to move from lower locations to higher ones without having to jump constantly.

The issue names no files, tests, or entry points. Start by tracing block geometry, collision handling, and player movement in the engine, then check how existing glass panes, slabs, or stairs are represented. Done would require a clear capability decision and documented or tested behavior for partial geometry, collision boundaries, and movement over ramps or stairs.