To be clearer then, you don't care (at least in the code) about all levels of parent->child->child relationships, you only want it to focus on the relationship for the current Page one is on?
Precisely. Originally, I was hoping to keep all top-level Pages visible in the sidebar (where this code is executing), but that seemed like more work, so I came to the parent-current-children model as what I thought was an easy fallback.
So, on the top level parent Page, you display parent and children, then on one of the child Pages (to the top level parent), you focus on the current Page as a possible parent to other child Pages, etc.
Right, except that I would like to show the parent for that current page as well. That's the reason I had the $parent code.
Does this read how you expect the code to work?
Yes, but it's not doing it. Take for example, this child-Page:
This first-level child displays the parent's title, but not its own.
Or this example:
This sub-sub-Page doesn't show anything!
I put my original code back in the sidebar file; your changes are temporarily commented out.