Copy and paste are handled by applications and the OS shell
Any program is free to define the formats it is willing to copy or paste - like mime types.
Software sucks, not because its bad, but because people wont implement things
Maybe I'm really dumb, but it should be obvious that replacing a section of rope in one knot with another, is intuitively not going to simply "add the unknotting numbers"
https://schmantics.blogspot.com/2011/12/third-circle.html