Please provide documentation on incremental devfile development

Users have asked how to build a workable devfile. The Support team has tried building them based on examples, starting with nothing and slowly adding content, starting with a full example and removing content, etc.

The results are frequently errors seen something like these:
"Failed to resolve a devfile. Failed to request factory resolver: Error occurred during creation a workspace from devfile located at...."
Most often more detail is given ("Error: (/apiVersion):The object must not have a property whose name is "apiVersion".") but these are inconsistent and seldom lead to success in editing the devfile.

Please provide a minimal viable devfile (the least amount of content guaranteed to work) so users will have something that 'should work'. If the devfile can be made workable without a project (so there is no source dependency), this is best because access to a source repository can sometimes be a significant challenge. If we have a minimal viable devfile that doesn't require anything outside the hosting cluster, that would allow validation of the base components and will remove some doubt about the fault being in the devfile or access to the source repository.

Please also provide some form of online editor so the user will not have to go through a change source / commit to source control / try the devfile / read failure message / change source / commit to source control / try the devfile / loop. (If we had some way to edit the proposed devfile before committing to source, that would be great.

Please discuss, ask for more details if the described scenario is not clear. The observations were made using a factory link, going against a github repository with a devfile. (Incremental changes to the devfile to try to pass the edit phase is frustrating.)