I'm not sure the outline rules are consistent between p192c and p96c, so there is that.
To me, a transparent wall is created by pixelling everything behind it normally, then putting the transparent wall in front of it. I use normal blending.
If the transparent thing has no solid frame, it needs an outline, and it stands to reason that this outline would be transparent as well. I don't think it has to be black in that case, rather share a tint with the object.
Attached is a glass pane asset from p192c. You can clearly see how anything behind the panes gets a bluish tint, and how it uses a semitransparent outline.
Though I'm sure there are many places where it would look off, and where a decision would need to be made on a case-by-case basis.