emerge-diff-ok-lines-regexp

emerge-diff-ok-lines-regexp is a variable defined in `emerge.el'.
Its value is

"^\\([0-9,]+[acd][0-9,]+$\\|[<>] \\|---\\)"

Documentation:
Regexp that matches normal output lines from `emerge-diff-program'.
Lines that do not match are assumed to be error messages.

You can customize this variable.