I consider myself to be both a good researcher and well-read. This topic, however, I had never heard of!
A colleague at work mentioned it to me, and when I mentioned it to my neighbour, Amy, I found that she had also not heard of it before.
Details can be found at www.diaperfreebaby.org, but the basics of the practice is as follows:
With a little monitoring, the parent can recognize how long after feeding/waking their baby needs to eliminate (whether liquid or solid).
The parent makes a trigger sound (something like “psssssssss”) when the baby eliminates, and the baby learns to associate “psssssssss” with eliminating.
Combining timing and sound, the baby will learn to eliminate on cue.
If it’s put into elimination position and it doesn’t need to go, it will squirm and must not be forced.