Here's a fast-food idea that might make Philadelphia mouths water:

Wendy's is planning to serve a burger with a soft-pretzel-like roll.

"The Pretzel Bacon Cheeseburger" is already "the buzz of fast food," says USA Today.

"This could be a very, very big deal," Boston University hospitality professor Christopher Muller is quoted as saying.

The pretzel burger did so well in limited testing that research analyst Mark Kalinowski of Janney Capital Markets recently recommended buying Wendy's stock, USA Today reports.

Wendy's isn't saying when consumers might be able to sink their teeth into one. A spokesman declined to divulge details.

The idea isn't entirely new, especially in Philadelphia.

PYT Philly at the Piazza ("Home of America's Craaaziest Burgers") has a $12 Cheesesteak Pretzel Roll Burger "on a bun baked for us at the Philly Pretzel Factory."

Philly Soft Pretzel Factory outlets don't sell burgers, but they do sell cheesesteak-stuffed pretzels, hot dogs and sausages encased in pretzel tubes, and open-face Pepperoni Melt Pretzels.

"Several years ago, Blimpie's rolled out a line of subs made with pretzel bread," reports USA Today. "And throughout much of Europe - particularly Germany - pretzel rolls of all kinds are extremely popular."

Pretzel rolls are also available at Wegman's. So you could always make your own pretzel sliders, bacon and/or cheese optional.

If Wendy's does produce the product, the question isn't whether Philadelphians will try it.

The question is: Do you put mustard on top, ketchup in the middle ... or both?