The hoagie is the Philadelphia word for the long-roll sandwich, and in Philadelphia the word is not loose. Elsewhere "sub" is a generic container that takes any filling and any treatment. In Philadelphia a hoagie implies a specific roll and a specific dress, and ordering one without saying more gets you a particular sandwich, not a blank format. That precision is the most local thing about it. The hoagie is less a recipe than a regional default: a seeded Philadelphia roll, cured meats and provolone or a tuna or turkey filling, and the dress is assumed unless you decline it. The city treats the build as settled, and the settled build is the identity.
The craft is in the roll and the dress, both of which Philadelphia has opinions about. The hoagie roll is its own bread: long, with a crust that has structure but yields rather than shatters, and an interior soft enough not to fight a layered, oil-slicked load down its full length. The meats and cheese are shingled, not stacked, so the slices interleave and every bite carries all of them instead of a band of one at a time. The dress is a system, not a set of toppings: shredded lettuce for an even cool crunch, tomato, raw onion, oregano, and a pour of oil that seasons and lubricates the interior so the cured meat reads as juicy rather than dry. Vinegar and hot peppers are the local options that sharpen it. Tomato is the moisture risk and goes in as part of the dressed structure so it does not flood the crumb. Built to the Philadelphia default, a foot of it holds together cold from one end to the other, which is the entire reason the format holds the city's loyalty.
The variations are the same roll under the city's own roster. The Italian hoagie shingles capicola, salami, and ham; the tuna and turkey hoagies keep the roll and dress and change the filling; the chicken cutlet hoagie runs a fried cutlet down the same bread. Each is a codified Philadelphia build with its own rules and deserves its own article rather than being crowded in here.