For creating a 1dArrayoutliner a first mockup is available.It was realized in 200 lines of code in the python language and shows the main window for an outliner. It is using a two pane layout. The user can select in the left menu the page and will see in the right pane the content of a page.
The page content is rendered with a self written parser. A pushdown automaton analyzes a markdown file and translates it into a rich text window. Right now, the GUI framework is wxpython but it seems that it is not powerful enough. So perhaps it makes sense to switch to tkinter?
The bottleneck of the current project is to save the information from the text editor into a markdown file. To realize it the text editor needs the abilty to save something as markdown, or the program needs to parse the information in the window manual. The task is needed because images and text are shown at the same time in the window.
That means, writing a text only outlier program is pretty easy, but if the images are shown inside th text it is much harder to program it.
Perhaps it makes sense to explain why there is need to program yet another outline editor. Because most of the programs from the past are very big projects It seems, that the average outliner / PKM software has at least a size of 1 MB and there is no upper limit so that current software has 200 MB and more.
The idea is to reduce the requirement to a minimum and write a much smaller outliner program which has 100 kb and less. For doing so there is need to specifiy which features should be implemented and which not. From a database persective an outliner has to implement the CRUD operations which stands for create, retrieve, update and delete. The interesting situation is, that more actions are not needed, if the user can add new pages and modify the existing he is happy. Editing a page means usually to enter text in the richt text window which includes adding images. I think it is not possible to ignore images and assume that a text only outliner will fulfill the needs of a user.