When it comes to airline ticket rules, the devil isn’t in the details. The devil is the details.

You’ll find the trouble in something called the “ticket tariff,” which is a massive, rambling and often incomprehensible document that passengers rarely see in its entirety.

Why? Partly because it tells you what you already know — for example, that you have to pay a fee if you want to change your ticket — and partly because it just doesn’t concern you. For instance, some tariff rules talk about special fares for police officers or firefighters, which a vast majority of passengers wouldn’t care about.

But there’s another reason why you won’t see the tariff rules: Airlines would rather you not know about them. That’s because they like to bury all kinds of restrictions in the fine print, hoping their passengers won’t read them until it’s too late.

“These rules are put there for one reason, and one reason alone,” says Rick Seaney, the chief executive of the Web site FareCompare.com. “To maximize revenue.”

To be fair, airlines and online travel agents do reveal some of the rules at the time of booking. But not always the way they ought to. Sometimes there’s a summary that glosses over key details, or you have to click on a link for more information, or the rules are WRITTEN IN UPPERCASE, which is a big turnoff because people think YOU’RE YELLING!

Of the 25 rule categories in the tariff, Seaney says there’s one every passenger should pay attention to before buying a ticket: Category 16, which covers cancellations and changes. I agree, that’s a big one. But there are others.

Here are my picks for the six worst ticket rules:

1. CANCEL ANYTIME — NOT!

Ticket rules are often contradictory. For example, here’s one called the “CANCELLATIONS ANY TIME TICKET.” You would think such a ticket would be cancelable any time at no additional cost, right? But you’d be wrong. The fine print says you’ll be charged a change fee. And if you happen to miss the flight because of unforeseen circumstances, you’re out of luck. The ticket’s no good, and you have to buy a new one: “NO CHANGES OR REFUNDS PERMITTED FOR A PASSENGER WHO NO-SHOWS,” the rule says. The fare also doesn’t allow for any upgrades on the day of departure. “I guess ‘any time’ doesn’t include the day of departure,” complained one airline insider who recently got snagged by this rule. “It’s terribly misleading.”

2. EVEN THE DEAD HAVE TO PAY FEES

When passengers die, airlines usually cut them a break. Sort of. Their next of kin can apply for a refund. But even in death, airlines have figured out how to make a little extra money. Check out this clause in one airline tariff: “NOTE — IN THE EVENT OF DEATH OF PASSENGER AN ADMINISTRATIVE SERVICE CHARGE OF USD 50.00 WILL BE ASSESSED IN ORDER TO PROCESS A REFUND.” The airline doesn’t want passengers to abuse this “perk” so it adds, “PROOF OF DEATH MAY BE REQUIRED.”

3. ONCE YOUR TRIP STARTS, YOU’RE LOCKED IN

Airlines love to slip this little clause into the fine print: “NONREF/CHGFEEPLUSFAREDIF/CXL BY FLT TIME OR NOVALUE.” Translation: If you try to make a change to your ticket after the first leg of your flight, you lose the ticket. And you have to buy a brand-new one. “The entire ticket is garbage,” says Bonnie Sherman, a travel agent based in San Diego, Calif. Most air travelers aren’t aware of this restriction until they try to make a change. By then, it’s too late.

4. THE CLOCK IS ALREADY TICKING ON YOUR TICKET

Think you have a year to use your ticket if you decide to make a change? Think again. “The large print says that if you cancel a nonrefundable ticket you have a year to reuse it, pay a change fee, and pay any increase in the ticket price,” says Bill Saavedra, a retired aerospace engineer who lives in Silver Spring, Md. “That’s wrong.” Why? Because the small print says: “WHOLLY UNUSED TICKETS ARE VALID PROVIDED TRAVEL COMMENCES WITHIN ONE YEAR FROM THE ORIGINAL TICKET ISSUE DATE.” Key phrase: “issue date.” In other words, you have less time to use your ticket than you think.

5. HERE’S YOUR NONEXISTENT REFUND

If you buy a ticket, some tariffs promise a refund under certain conditions. You might find something in the fine print that says if a fare decrease occurs after a ticket is bought, “THE DIFFERENCE IN FARE MAY BE CREDITED.” The operative word here is “may.” Some airlines will charge a change fee and will issue the balance as vouchers, which is not at all what you would have expected. Bottom line: Don’t just read the tariff, but review the airline’s policies, which can contradict or invalidate its rules.

6. SO MUCH FOR FAMILY VALUES

Bereavement fares, which are special fares for family members traveling because of “the death or imminent death” of a relative, are said to be on the verge of extinction. They haven’t expired yet, but there’s a catch. Airlines take it upon themselves to define what family is — and isn’t. The death in question must be of an immediate family member, defined as a “SPOUSE/COMMON LAW-SAME SEX, CHILD/ADOPTED, STEP- GRAND- GREAT GRAND- LEGAL INLAW, COMMON IN LAW, DAUGHTER/SON/MOTHER/FATHER/LEGAL, INLAW, COMMON INLAW.” Did they leave anyone out? Well, yes. Under this relatively narrow definition, I wouldn’t be able to attend the funeral of my brother, sister, niece, nephew, aunt, uncle or godfather. But thanks for the condolences.

These are not extreme examples. Unexpected charges and fees are to be found buried in every airline’s ticket tariff, and some say they are bad for business.

“The more times they encounter the words ‘charge’ and ‘collect’ in the rules, the angrier passengers become,” says Garth Corey, a consultant in Albuquerque, N.M., who got burned by one airline’s ticket tariff. His solution? He took his business elsewhere.

“That’s the real cost of the fine print to airlines,” Corey says. “The airlines that do this will pay for their arrogance.”

Airlines, listen up.