You’re free to use whatever numbering scheme you want as long as it gives the correct output. There is no preferred way that I know of, and this is good – needlessly limiting people’s ability to produce the desired output serves no purpose and can even be harmful: Too many rules alienate users from writing posts, and that’s definitely not what we want.
As the output shows, there is absolutely no difference between a list numbered with any 0 or 1
0.
0.
0.
and a list using the actual numbers that appear in the output as well:
1.
2.
3.
The first number you use is the starting number for the list (but both 0 and 1 give 1), so to begin with 4 you could do 4., 5., 6. or 4., 4., 4. or even 4., 0., 10., the output is the same. In the case of your answer the editor just wasn’t fully aware your syntax was fine.
Ask Ubuntu’s formatting help page is a single page with everything you need to know about markdown by design; let’s keep it as simple as possible. It says:
A numbered list:
1. Numbered lists are easy 2. Markdown keeps track of the numbers for you 7. So this will be item 3.
I’d say this means essentially what I wrote above: Output matters, the rest is up to you.