What is Chinese Brown Sauce Made Of?

Brown sauce: the beloved basic in every Chinese take-out joint in America. But what's in it? It seems like there's a different recipe wherever you look—for example, compare the recipes found at Eat Close to Home, Epicurious, and Rasa Malaysia. Besides the requisite soy sauce and oyster sauce, I found variations including beef broth, corn starch, potato flour, Hoisin sauce, ketchup, and, oh, about five hundred other ingredients. At food blog The Heavy Table, Kelly Hailstone tries to find out what brown sauce is made of by calling local Chinese restaurants, but finds no answers. Even her own mother, a native of Hong Kong, wouldn't tell her.

I'm not really looking for the authentic stuff here, just the sauce I find on my $5 lunch special from Monday to Friday. Has anyone ever figured out what's exactly in this generic binder of chicken and broccoli?