Thanks for your detailed response again, Lal. That’s very helpful. It actually led me to a deeper understanding of jhana samapatti.
Ajahn Brahm is from the Thai Forest tradition and this is how he was taught by Ajahn Chah. So it’s not just him. Many Theravidians know of this technique. He describes the step-by-step process in his book I linked to above. The stopping of the breath in the 4th jhana is also clearly stated, which coincides with what I’ve read from the posts here. When they come out of the meditation they can recall what happened. Just not during the meditation. I wonder if that would be possible if it’s a kind of asañña samadhi.