Hello, This is another update about the status of the patch. I am mostly happy with the current state of the code, got rid of most of the bugs, and did not get any new bug reports in github for a while. I would like to start the process of applying the patch on master. As a first step, I would like to submit the core folding library (org-fold-core) for review. org-fold-core is pretty much independent from org-mode code base and does not affect anything if applied as is. It will be used by org-specific org-fold.el I will finalise and send later. For now, I would like to hear any suggestions about API and implementation of org-fold-core.el. I tried to document all the details in the code. Looking forward for the feedback. Best, Ihor