For the sake of sharing, here is sample code that I just tested on Inform 7 build 6M62:
"GlkWindowLearning1" by "Community".
The story genre is "Other". The release number is 1. [genre: https://intfiction.org/t/defining-the-story-genre/4615/1 ]
The story headline is "Glulx technical demonstration". [ This is all about pure Glulx, not Z-Machine due to extension. ]
Include version 15/161003 of Flexible Windows by Jon Ingold.
[DEPENDENCY: Simple Graphical Window automatically includes Flexible Windows by Jon Ingold]
[Include version 10/161003 of Simple Graphical Window by Emily Short.]
The side-window is a text buffer g-window spawned by the main window.
The measurement of the side-window is 30.
The position of the side-window is g-placeright.
Rule for refreshing the side-window:
say "[bold type]Side-Window[roman type]";
try taking inventory;
When play begins:
open up the side-window.
[If user picks up item, the side window inventory needs refreshed. Brute force approach is to do it every single turn regardless if the user actions altered inventory.]
Every turn:
refresh side-window.
Place is a room. "You can go west. You can try 'drop flask' to see if the Side-Window reflects changes."
Western World is west of Place. "You can go back east."
A petri dish is carried by the player.
A flask is carried by the player.
A wallet is carried by the player.