Murphy, Lynne (2018-03-29) (英語). The Prodigal Tongue: The Love–Hate Relationship Between British and American English. Oneworld Publications. pp. 211. ISBN978-1-78607-270-2. https://books.google.com/books?id=uh69DwAAQBAJ&pg=PT209. "...the British are so particular about sandwiches that they use the word less than Americans do. In Britain, a sandwich is some filing between two slices of bread. Not a roll. Not a bagel. Not a baguette. Without sliced bread, it's not a sandwich. The American sandwich prototype is much like the British: savoury filings within two slices of bread. But American sandwiches are allowed to wander further from the prototype, because they interpret the 'bread' requirement more loosely. An American sandwich can be on a roll, on a bagel, on a bun, on a croissant, and at breakfast time, on an English muffin..."
