Does intentionally swallowing mucus flowing from the nose or phlegm invalidate the fast?

Swallowing phlegm does not invalidate the fast according to the most preponderant opinion of the scholars, because it originates from within the body and is neither food nor drink. Swallowing it is not considered like swallowing something from the outside, such as a pebble. Nevertheless, it is disliked to swallow it if it is possible to expel it. One should also consider the differing opinion of those who invalidate the fast by swallowing it, so that the fast remains valid by consensus.