We would llike to have additional button in the RTE along side the existing ones which would allow to insert an "expander/drawer" in to the body of article/case ( talking i KM conext here but can apply in general)

This is an example to show the idea that we are going for. They would like to have a single case/article, which contains the content, and can include expanders, and sub-expanders. This is NOT the styling that we are looking for on the website, but rather the structure. sample screenshot from youtube help pages