The json is the clipboard data you can directly paste into construct 3 layout
Viewing post in 3D Buildings and Level Editor for Construct 3 comments
In my test project above, I pasted code.txt into the event sheet and material.txt into the layout.
However, the saved file from the editor, the project.json file contents, won't be pasted into a layout, which I think makes sense since it is not in c3 clipboard format. It starts with:
{"c3save":true,"version":1,"rt":
I'll wait a bit for the bug fix, doc/tutorial.