Posted by xcoulon on Nov 10, 2019; 8:50am
URL: https://discuss.asciidoctor.org/nest-inclusions-with-level-offsets-tp7341p7344.html

Ohhh, I found my mistake! I did not include the right file from the beginning (facepalm)
Running again with the correct file inclusions, I get the expected result (with leveloffsets being accumulated):

asciidoctor -o - tmp/test.adoc | grep -e "<h\d"
<h1>main title</h1>
<h2 id="_parent_title">parent title</h2>
<h3 id="_child_title">child title</h3>
<h4 id="_grandchild_title">grandchild title</h4>

Thanks for your response and your time to reproduce and verify, @habamax!