stem in title not parsed

[edl7878]

Title of asciidoc:

=== stem:[Set] product

downdoc output markdown title:

### stem:[Set] product

[mojavelinux]

Only attributes are expanded in section titles and discrete headings. No other substitutions/translations are applied. So in order for this to work, substitutions would need to be applied to the heading text.

[edl7878]

adoc:

[subs="normal+"]
== stem:[a/b]

output md:

## stem:[a/b]

seems no effect in heading...

[mojavelinux]

substitutions would need to be applied to the heading text.

I meant they need to be applied in the downdoc code, not in the source AsciiDoc.