The part after ///attributes:
is a fully html compliant attribute (but without the quotes).
So instead of writing
<ol style="list-style-type:none">
<li>LIST ITEM 1</li>
</ol>
we write (as md):
///attributes:style=list-style-type:none
1. LIST ITEM 1
In this case a CSS style is used but you can also use other attributes like this:
///attributes:class=para-class
and then adapt your style sheet accordingly (for instance at the beginning of a md page). It's also possible to have a comma separated list of attributes.
At the end I just invented an own block for markdown-it!.
Look also at the following article:
And here is the documentation for the ready-to-be-used plugin!