When Amy Ray of the Indigo Girls works a crossword puzzle, she sees a metaphor for songwriting, finding just the right word that fits. When former President Clinton sits down to a puzzle, he sees an analogy to how he solves problems — "You have to find some aspect you understand and build on it," he says.

And for Ken Burns, the PBS documentary-maker who loves to make every subject as grandiose as possible, the crossword puzzle isn't just black and white squares in the newspaper, it's "an iconic manifestation of civilization."

Fit that in your four-letter space.

Just as champion spellers have had their day with the documentary "Spellbound" and the recent prime-time National Spelling Bee, now it's the turn of those who like to think inside the box, the 50 million or so Americans who regularly work crossword puzzles. (For those who came in late, they're sort of like sudoku, only with letters instead of numbers.)

They have "Wordplay," a documentary hit at this year's Sundance Film Festival that opens in Tucson July 14. Among the movie's stars is former Tucsonan Merl Reagle, a crossword creator whose puzzles appear in Caliente each Thursday. Clinton, the Indigos, Jon Stewart and other celebrity cruciverbalists are also featured, along with scarily brilliant speed-solvers from all walks of life who gather once a year in Stamford, Conn., at the American Crossword Puzzle Tournament.

"You don't have to be fabulously good to go to the competition," says Julie vonHaam, 66, of Reynolds Plantation, the Lake Oconee golf community near Atlanta. She has attended twice. "I'm not good like those elite people, but I'm probably better than most people."

Bruce Kahn, a technical editor at IBM in Atlanta who has competed many times at the tournament, agrees with the consensus of puzzlers that these days, it's not about knowing obscure three-letter words for a river in Africa, but deciphering fiendishly misleading clues, instead.

"There's more wordplay involved," he says. "It's not only fun, but you get a lot of satisfaction from figuring it out."

Responsibility for that change from rarefied nouns to clever clues goes to Will Shortz, crossword editor of The New York Times, founder of the American Crossword Puzzle Tournament and basically The Man when it comes to crosswording today.

"If you look at crosswords 30 years ago, there were a lot of obscure references in them," he says. "Nowadays, if you solve the Times crossword, you are familiar with everything in the grid. The clues are tricky sometimes. They are fresh. There's not much to look up."

"The old joke," Shortz adds, "is crossword puzzle solvers are people who have too much time on their hands. Whereas crossword solvers tend to be the busiest people, like Bill Clinton. Here's a guy who's probably nonstop from dawn till the time he goes to bed and if he gets a five- or 10-minute window, he'll squeeze a crossword puzzle in there just to keep his mind active."

The mental activity of puzzle-solving is frequently cited by fans as a way to stave off senility or Alzheimer's disease. The scientific research for these claims is inconclusive, but that doesn't deter Shortz.

"I'm absolutely certain that crossword solving will keep your brain sharper throughout your life," he says.

As with any group of people who do one small thing somewhat obsessively, there is a tendency, even among some puzzlers, to refer to themselves as nerds.

"The tournament attracts a lot of people who are kind of the stereotype nerdy people," says Atlanta puzzler Kahn, "but on the other hand there's people there who enjoy talking about other things."

"Overall, crossword fandom ranks pretty high in the hierarchy of nerdy hobbies," offers Tim Collins, author of the upcoming book "Are You a Geek? 103 Ways to Find Out."

"Although lots of normal people can happily slip a quick crossword into their morning routine, it's the kind of pastime that invites obsessive fandom."

His checklist for the line between crossword fan and crossword nerd includes attending tournaments, timing yourself, and working in pen rather than pencil, which includes pretty much everyone in the movie "Wordplay."

Although crosswords are still considered the gold standard of puzzles, the recent phenomenal growth of sudoku — the Japanese fill-in-the-numbers grids — has some fans somewhat puzzled.

The last crossword tournament, held in March, added a "Sudoku Smackdown" one night.

VonHaam played along but says a lot of puzzlers thought sudoku was just a fad. "People felt it would go the way of Rubik's Cube," she says. "Ten years from now, who's going to be doing those puzzles?"

Puzzle facts

● More than 50 million people in the United States work crosswords regularly.

● Crosswords almost always have an odd number of squares on a side. Why? So there can be a single square in the middle, for symmetry.

● The largest crossword ever was 64,371 words, in Russian, in 2004.

● Most common answer: era

● Most common four-letter word: area

● Most common five-letter word: erase

● History: The first crossword puzzle appeared in the New York World in 1913. The New York Times started its crossword in 1942. The American Crossword Puzzle Tournament started in 1978.

— Source: "Wordplay: The Official Companion Book."