mfX
Each minefield has an own, "local" friendly code (as above). In addition, you can define a "universal" minefield friendly code. For this, set a planet to mfX, where X can be any character. Ships can then also use this code to achieve a friendly code match with your minefields, for example to safely pass through them.
This is useful when you want to grant a (not-yet-)ally free flight through your minefields without granting him access to your planets.
mfX is not considered a special friendly code that is exempt from Friendly Code Matching (because it is actually intended for matching).
When several planets owned by one player have an mfX friendly code, the planet with the highest Id number specifies the universal minefield friendly code. When Bird Men try to change a planet's friendly code to mfX using Super Spy Deluxe, that will trigger an Ionic Pulse to decloak ships orbiting that planet (if possible, see mission description).
