Definition Lists and number of spaces

I haven't looked at this in a long while but I notice that definition lists require multiple spaces (3) after the colon to work.

In the following markdown the first block works, the second block does not:

First Term
:   This is the definition of the first term.

Second Term
:   This is one definition of the second term.
:   Continues previous term

---

First Term
: This is the definition of the first term.
: This is the definition of the first term.

Second Term
: This is one definition of the second term.
: This is another definition of the second term.

Babelmark seems inconclusive on this with a whole bunch of parsers (including Markdig in that test) failing to render either block:

https://babelmark.github.io/?text=%23+Test+Item%0A%0AFirst+Term%0A%3A+++This+is+the+definition+of+the+first+term.%0A%0ASecond+Term%0A%3A+++This+is+one+definition+of+the+second+term.%0A%3A+++Continues+previous+term%0A%0A---%0A%0AFirst+Term%0A%3A+This+is+the+definition+of+the+first+term.%0A%3A+This+is+the+definition+of+the+first+term.%0A%0ASecond+Term%0A%3A+This+is+one+definition+of+the+second+term.%0A%3A+This+is+another+definition+of+the+second+term.%0A

and quite a few - including PanDoc parsing both blocks.

All parsers seem to recognize the Definition List though because all parsers are generating the headers properly - it's the sub items that are falling through.

Is there a reason that Markdig requires the extra spaces? The parsers that do render the list properly don't require the extra spaces.

Start by reproducing the two definition-list examples from the issue with Markdig and compare their rendered output with the referenced Babelmark results. Determine the intended spacing behavior, then add regression coverage for the agreed syntax and confirm that the affected definitions render correctly.