(Entertainment Weekly) -- There are many documentaries about the fashion world.

Anna Wintour, editor-in-chief of American Vogue, attends a screening of "The September Issue" in New York.

Some, like "Unzipped" (remember when Isaac Mizrahi was the new black?), are impish fun, and a few, like "Valentino: The Last Emperor," have been marvelous.

But the singular fascination of "The September Issue," R.J. Cutler's lusciously revealing fly-on-the-wall portrait of Anna Wintour, the editor in chief of Vogue, doesn't hinge on clothes, or glamour, or the sprinkle of stars on display. (Look, it's Jean Paul Gaultier! And Sienna Miller!)

It begins with the electromagnetic pull of power.

We expect to see Wintour hidden behind her famous sunglasses, as indomitable as the Sphinx. But Cutler, the producer of "The War Room," opens the movie with Wintour un-spectacled, her face pert and pretty, gazing with a twinkle as she explains that those who look down on fashion people for being ''shallow'' feel threatened by them.

It's an astute point, and Wintour makes it in a way that's so direct and amused -- eager to defuse her mystique, which of course only adds to it -- that even when ''exposed'' by Cutler's camera, she's still a sphinx, impassive but for the occasional hint of a wince or a soft smile.

Her mind is always in two places at once: on the task at hand, and attuned to the global fashion ramifications of every move she makes.

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In "The September Issue," we observe the process by which Wintour and her vast army of editors, designers, photographers, models, and gofers labor, throughout the summer of 2007, to assemble Vogue's massive September issue, a plush treasure chest of ads, photo spreads, and gilded dreams.

It's through Vogue that Wintour, more than any other figure, reigns over the decisions -- of taste, aesthetics, economics -- that shape the $300 billion-a-year fashion industry.

The September issue is more than a magazine. It's a major motion picture stuffed between glossy covers, with Wintour as its all-knowing, all-dictatorial producer. She pulls the whole issue together, keeping her eye on the big picture while micromanaging the small ones, like David O. Selznick presiding over the production of "Gone With the Wind."

Is she a diva, a bitch? The devil in Prada? (If my eyes don't deceive me, she seems to prefer Lagerfeld.) Well, she's a devil only if you think there's something nasty about a woman who's paid a royal salary to elevate her every whim into a command.

"The September Issue" is organized so that we observe the ruthlessness, the high perfectionistic logic, of each decision Wintour makes. There's not enough color in that collection! Why does this layout feature only one fur garment? -- it looks out of place!

"I don't see any real evening on that rack," she tells a quivering Yves Saint Laurent designer. No casual comment about after-dark wear was ever such a threat. Yet Wintour isn't mean; she simply means what she says.

If she were just pushing people around, we might look on with derision (or fear), but part of the movie's dishy fun is that there's room for more than one ego in the room.

André Leon Talley, who is Wintour's consigliere and editor-at-large, is a bitch (I mean that as a compliment), a witty postmodern man so neurotic about swaddling his giant physique that he can't play tennis without draping a designer towel over his shoulders.

And if Wintour is the film's subject, its true heroine is Grace Coddington, Vogue's passionate and addled creative director. A former model (like Wintour herself) who rose up in the 1960s glory days of swinging London, Coddington now looks like a Pre-Raphaelite ghost. It's she who orchestrates the magazine's photo shoots, which are like eroticized couture dioramas that fuse the past and the future.

When one of Coddington's spectacular spreads gets cut, she sulks with fury. We see why she's mad -- every image she creates is gorgeous -- yet Wintour isn't out to destroy. She simply has priorities, of mix, balance, and (yes) money, that keep Vogue thriving.

These two square off like jungle predators, but they need each other; they create a yin and yang of commerce and beauty that Vogue melds into that indefinable thing called glamour.

I came away from "The September Issue" liking Anna Wintour more than I thought I would, but mostly with an appreciation for her mission: not just to sell magazines, to market clothing and style, but to give femininity its sheen.

EW Grade: A

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