What does the corner line of the tangent line bleeding line mean in graphic design?

Knives are generally used to cut packaging and adhesives. Generally, the position of cutting line is determined after the design is completed, and the packaging design has bleeding line and alignment line.

3mm bleeding corner line cutting line is used for color pages and sample albums. Bleeding should be considered in the design. For different printed materials, if it is a single page, bleeding should be added on all sides, and so on. Pre-press information such as corner line cutting line should be added when making up.