There are so many rules for a Disney princess. Too many for Disney’s newest princess, the Scottish heroine Merida in “Brave,” to remember.

“A princess does not doodle,” her mother lectures in a light Scottish burr. “A princess does not chortle.”

“A princess does not stuff her gob.”

“A princess does not raise her voice.”

But here’s the one that makes the fiery redheaded archer snap:

“A princess should not have weapons.”

Pixar’s first “Disney princess” completes the evolution of the studio’s distinctly American take on young womanhood.

Princesses have evolved from sailor-obsessed mermaids to Merida, a spunky, self-assured lass who’d rather eat an arrow than take up with some guy her parents point her way. She has duties, obligations, an arranged marriage to endure.

Her mother, Queen Elinor (voiced by Emma Thompson), may insist “We can’t just run away from who we are.”

But as Merida narrates, her fate should be her own.

“Destiny — it’s the one thing we search for, or fight to change.”

“Brave” is a spirited Scottish-accented romp that packs female empowerment into a generally amusing tale of youthful impulsiveness and its consequences. The writers and animators blend the oafish, brawny Scots humor of “How to Train Your Dragon” with the magic of “The Secret of Kells” into a story about being brave enough to change your fate.

Merida (Kelly Macdonald of “Nanny McPhee” and “No Country for Old Men”) seizes her destiny when her father (Billy Connolly) and mom start parading unsuitable suitors before her, a marriage that will keep the peace among the Scottish clans. As tradition would have it, the would-be-kings compete in feats of strength to win her hand. But she selects one sport where she herself dominates. She hopes to win her independence with the draw of a bow.

Her mom says “Nothing doing.” So Merida takes her case to a witch, which is how mum gets turned into a bear. And since this is the bear-hunting-happy corner of Scotland, that’s when “Brave” tumbles, delightfully, into slapstick.

Bear gags pile up, and I love the way the animators turn the queen into a critter who can’t shake her dainty manners, or sense of decorum, even in ursine form. Merida has to protect the mother she quarreled with and endangered from a castle-full of burly Scotsmen who want a trophy for the castle wall.

Merida’s helpmates in all this are her mischievous younger brothers, three wee hellions with can-do attitudes about any prank, hurling themselves (without dialogue) into the mayhem.