Related to classifications further down Ryan's thread: consistent taxonomy would appear to require, based on his "a burger has one hole" corollary, that a hoagie, a hot dog and a taco all have the same number of "holes"

There is an as-yet unnamed category of foodstuff which has a long opening on one side and two smaller openings which includes taco, hot dog, gyro, meatball sub and hoagie

There is another category of foodstuff in which the bread is circular so there is technically only one "side" for the opening, which includes burger and quesadilla

No, and the fact that we also call it a "sub sandwich" indicates that it is a variant