Draw on screen border in Commodore 64

Question

I have this curiosity for 25 years and I would love to understand the trick.

In the Commodore 64 the border was not addressable by the 6569 VIC. All you could do was to

Answer 1

You can also get sprites to border in basic: BASIC Sprites in Border

iirc, there was also some way to confuse the video chip so, that it draws 26th line of text.