Hello, is it possible to add hypertext links with plot.tree without using a JSON file like on this notepad Radial tidy Tree with hyperlinks / Heziz's Workspace | Observable ?
For this one : Néguentropie / Pixflowave | Observable
The short answer is, yes, it’s possible. I’ve created several notebooks that use TippyJS to create interactive tooltips on a visualization created with Observable Plot. This map of Italy, for example. While that example does use JSON to store the information, you ultimately need to write a function that translates information that you can get on hover into the tooltip. You could certainly build such a function that accepts the text strings in the SVG and returns the tooltips that you want. How you do that really depends on what type of information you want in the tooltip. It seems likely, though, that you’d want to retrieve some information from a data file of some sort.
Thank you for your response, I had also seen your notepad. I found this one in the meantime which shows that you can query a CSV file. Link Tree / Pixflowave | Observable
My situation is that at the moment I don’t have any data built or compiled yet. So I enter it in a cell as my knowledge progresses which goes piano piano 
I am therefore looking for a solution close to that which we can have in Markdown. link