He spoke of this in one of his comparative study courses of the Agamas and Pali discourses back 2011–2104 through the University of Hamburg. The links for those lectures are available on line (and have been posted on this forum too), but offhand I don’t have them.
To expound a bit on what @Javier said, my recollection of what Ven Analayo said in the lecture is that one could be fully inside a jhana but then inadvertantly pop out for a moment, so to say, upon for example, hearing a loud sound if the state was not fully stable (and he gave an example from the discourses of a time this happenned to Ven Moggallana). He then said it was kind of like someone being fully submerged in a pool of water, both head and body, vs. being completely out of the water on the shore, but then asked what if one’s head pops out for a moment but the body remains under the water, and said that it’s a little difficult to say whether the person is in the water or out of the water. So while the person is clearly not fully submerged in the water(i.e. fully inside the jhana at that moment of popping out due to some temporary disturbance/instability in the state) she’s also not fully out of the water and may then return to fully submerged (i.e. fully inside the jhana).