ediff-diff3-ok-lines-regexp

ediff-diff3-ok-lines-regexp is a variable defined in `ediff-diff.el'.
Its value is

"^\\([1-3]:\\|====\\|  \\|.*Warning *:\\|.*No newline\\|.*missing newline\\|^
$\\)"

Documentation:
Regexp that matches normal output lines from `ediff-diff3-program'.
Lines that do not match are assumed to be error messages.

You can customize this variable.