Minor-ish spoilers ahead.
In Split (2017), Casey tries to persuade Hedwig, the 9-year-old personality of Kevin, to help her out of the room she's imprisoned in, because Hedwig seems to reveal the location of a window. However, to her disappointment, it's revealed that the window is just a pair of drawings.
Everything Kevin's personalities do, and even the very reason for their existence, is because of the abuse he went through as a kid. Denis, for example, "came into light" because of Kevin's dire need to keep everything spotless and clean. Hedwig seems to be the cool kid Kevin wishes he was.
There is extra emphasis on the window drawings; they even affect the plot. Hence, they can't be just like other random drawings of Hedwig. He even took the extra work of drawing one closed and one open window, to further simulate a real one.
Why did Hedwig draw a window? What was its significance to him? I imagine it had something to do with his childhood, like being grounded in a window-less room, like a solitary confinement. Or it could be less complex; he wanted a normal-sounding room, one that could have a tape player besides the window.
Was this ever addressed by director Shyamalan, or anyone else? I couldn't find anything by few simple searches.