Does swallowing the acidity or acidic liquid that comes out of the stomach and reaches the mouth invalidate the fast, given that it is from food?

If something comes up from the stomach to the mouth, and it was possible to spit it out, but the fasting person intentionally swallowed it, then their fast is invalidated. However, if it did not reach the mouth and then returned to the stomach, the fast is not invalidated by that. The reason for invalidation is not limited to food; it also includes vomit, phlegm, and anything similar. The mouth is considered an external area, and breaking the fast occurs with anything that reaches it.