Which existing buttons are being removed from the stack view?

In chapter 17 and 18, in a couple occasions (pages 362, 374) it is mentioned that “the existing buttons need to be removed from the stack view and the new buttons need to be added”. Where exactly does the stack view get the “existing buttons” added because I cannot find anywhere where this happens, and by checking the value of “oldValue” in the property observer, this array does not appear to have anything at all. Could anyone clarify this for me, please?

Additionally, on page 374 on the last paragraph it says “The imageButtons property stores the images”, shouldn’t this be referring to the images property instead?

These two things may seem very trivial but they are really confusing to me, I’d really appreciate any comments regarding this.

Thank you!