Why does CommonMark consider this 7 space indent a code block?

I'm storing some notes with CommonMark and I noticed that this snippet seems to render differently on SO (echo is indented 7 spaces).

1. Print Windows folder path

       echo %windir%

Here it is interpreted as a code block on http://spec.commonmark.org/dingus/:

And here it is on Stack Overflow:

If I indent echo by 8 spaces instead, it will now show as a code block on Stack Overflow:

But on http://spec.commonmark.org/dingus/ it now has a leading space (I've selected it to show):

Is this because SO isn't actually using the full CommonMark spec (yet?)?

Or is there a CommonMark setting to make it render the way SO does?

This is a little annoying because many of my notes are indeed text that could find their way into a question or answer somewhere on Stack Exchange. So I'm just hoping to figure out what's going on here.

Turns out this was answered by @balpha in this June 2015 post:

https://meta.stackexchange.com/a/258587/879

List items

Currently, this will create a list item with two paragraphs:

1. This is the first paragraph

 And this is the second one.

With CommonMark (and even in a significant number of other Markdown implementations), the "second one" will not be part of the list item, but a stand-alone paragraph after the list. To make it part of the list item, you have to indent it to the same margin as the first paragraph like this:

1. This is the first paragraph

   And this is the second one.

I was confused by what seemed like a somewhat arbitrary "7 spaces" but now I realize it's in fact 3 spaces to bring it under alignment with the list item, and then the standard 4 spaces which identifies it as a code block.

Confirmed by this little test:

This actually makes good sense to me, I think I like it.

So that answers that, I guess SE still uses its own variant that doesn't involve this type of alignment.