One of the tropes of Emacs use is the idea that there’s always something new to learn about the editor. I know that to be true but today it was brought home to me by a new video from Protesilaos Stavrou. The video is nominally about managing window placement but part of that is the notion of “side window.”
I had never heard of them before or even the concept that they implement. It’s no wonder. While I was preparing to write this I looked them up in the documentation but couldn’t find anything at all about them in the Emacs manual. I had to consult the Elisp manual to find any information about them.
The problem that Stavrou is seeking to solve is the inconsistent placement of the windows that pop up for things like HELP. Sometimes a new window is created; other times an existing window is reused. If you’re like me, you probably suspected that the behavior is configurable but haven’t seen or used the mechanism to do it. Window placement configuration is fairly fine-grained so you can pretty much have it anyway you like.
Unless you’re very particular about window placement or want to implement something like emacs-dir-treeview, you probably won’t need to deal with side windows or the other functionality that Stavrou discusses but his video does show how the configuration is possible if you need it. The video is just short of 19 minutes long so plan accordingly.