If your package cannot coexist with other packages (because of file conflicts, runtime incompatibility, etc.), list the other package names in the CONFLICTS variable. You can use shell globs like * and ? here. Packages names should be enumerated the same way they appear in /var/db/pkg. Please make sure that CONFLICTS does not match this port's package itself, or else forcing its installation with FORCE_PKG_REGISTER will no longer work.
Note: CONFLICTS automatically sets IGNORE, which is more fully documented in Section 12.19.