Where is the code for the function under c in Screen's copy-mode?

Question

This question is based on the thread.

I am interested in the function under the button c because of my current interest in the similar function in the column detection of OS X S.Leopard's Preview.

Where is the code for the function under c in Screen's copy-mode?

Answer 1

In the source, in mark.c, starting on line 733.