This:
. Level one.
.. Level two.
How do I get back to level 1?
. Back to level one.
will result in this:
1. Level one.
a. Level two. How do I get back to level 1?
2. Back to level one.
But how can I accomplish this:
1. Level one.
a. Level two.
How do I get back to level 1?
2. Back to level one.
So that "How do I get back to level 1?" is indented the same as Level one.?
The following should work:
. Level one.
.. Level two.
+
How do I get back to level 1?
. Back to level one.
Note the blank line and the lone +: these shift the list level one back, whilst attaching the next paragraph to the previous item.
See the AsciiDoc writer's guide on asciidoctor.org, about attaching to an ancestor list:
You may find that you need to attach block content to a parent list item instead of the current one. In other words, you want to attach the block content to the parent list item so it becomes a sibling of the child list. To do this, you add a blank line before the list continuation. The blank line signals to the list continuation to move out of the current list so it attaches the block to the last item of the parent list.
...
Each blank line that precedes the list continuation signals a move up one level of nesting.
The above renders in my browser as
1. Level one.
a. Level two.
How do I get back to level 1?
2. Back to level one.
and in HTML as
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Level one.</p>
<div class="olist loweralpha">
<ol class="loweralpha" type="a">
<li>
<p>Level two.</p>
</li>
</ol>
</div>
<div class="paragraph">
<p>How do I get back to level 1?</p>
</div>
</li>
<li>
<p>Back to level one.</p>
</li>
</ol>
</div>