But after “Pretty Woman,” it’s been basically some variation on the Cinderella story, with some lip service to feminism thrown in.

Sexiness is good, but having sex is problematic (Rule No

ROMANTIC COMEDY heroines aren’t characters anymore, they’re tranquilizers. They’re designed to fan the fantasies, soothe the disappointment and calm the frayed nerves that come later. And to do that, they must be built to specifications.

How? After watching “Monster-in-Law,” I canvassed a few writers — who won’t be named, so that they may continue to write and happily incorporate notes — to share directives they’d received while creating their romantic heroines. There is no such thing, it appears, as a romantic comedy heroine who couldn’t benefit from being just a little more “likable” than she already is (Rule No. 1). “Likable” of course, can mean many things in the real world;

but for a studio it tends to mean that she does some kind of work involving animals or the elderly. Perhaps she’s a veterinarian, or a zookeeper. If she works in business, she has a boss who doesn’t appreciate her, or steals her ideas. Whatever it is, she has it tough. Sometimes she’s a single mother, “trying to hold it all together in this tough, dog-eat-dog world,” one writer offers. “Also, likable often means clumsy,” she adds. “She falls down a lot, but in an adorable fashion. Likable also means pretty. As we all know, the fat are unlikable.”

They can be sexy, adorable and even seductive but we don’t want to think they’re kinky or overtly sexual in any way

Once she’s been established as almost unbelievably likable, a heroine must be “sympathetic” (Rule No. 2) because, what if she got so likable people actually started to hate her? She must be punished for her smug likability — dumped, cheated on, left at the altar. (When a male character leaves a girl at the altar, he’s an irredeemably evil cad. When a female character does the same, she’s Julia Roberts.) Also, it’s not a bad idea to smite her progenitors in some way. Dead mother and lonely father are a good way to go. The exchange, according to another writer, might go something like this:

“ ‘We need to see the character’s vulnerability’ is a note you get a lot,” another writer says. A girl who is left at the altar does not walk away unscathed. There are emotional repercussions of a very real nature. “This means to add moments where the heroine stares out a window as it’s raining, or we see her in her pajamas eating Haagen-Dazs out of the carton.”

While it’s OK to spend some time with Ben Jerry, heartbreak does not call, under any circumstances, for excessive, depressive or erratic behavior of any kind (Rule No. 3). The jilted heroine will not indulge in unflattering self-destructive action such as drinking too much or indulging in a sordid rebound. Ice cream is fine, but there are limits. “I was once given the following note by a producer,” another writer says. “ ‘Can you not have the character eating so much? It makes her feel a little piggish.’ The character was eating in three scenes.”

Essential story elements can and should be jettisoned if they risk making one of the female leads less attractive than she otherwise might be (Rule No. 4). “I wrote a romantic comedy about three couples all dealing Cougar dating service with pregnancy,” a writer says. “The film wasn’t really about being pregnant but about how their pregnancies affected each of their relationships. The note from the exec: ‘Why don’t you make it so they aren’t pregnant, because pregnant women aren’t very sexy.’ ”

5). How much is too much? As one writer I spoke to puts it, “Sexuality is a no-no for romantic heroines. When it looks like they’re about to really get it on, suddenly they’ll innocently pass out because they drank too much, like in ‘Working Girl,’ ‘Two Weeks Notice.’ ”