Chunking topic in the specification

[Robert D Anderson <robander@us.ibm.com>]

Hi,

I was editing the chunking topic in the Architectural specification this
evening, based on review comments posted to the wiki. One of the comments
from Eliot is this:
>> "Topicheads and [implicit] title-only topics": this topic is I think
covered sufficiently in the main discussion of the chunk attribute under
the entries for to-content and to-navigation.

There is a section in that topic with this title, but the contents are
empty. Well - not quite - they've been replaced with a processing
instruction:
<section id="section_AAD228491B514AC69EAC5F7C0ED1C7BE"><title>Topicheads
and [implicit] title-only topics</title><p><?xm-replace_text Paragraph?>
</p></section>

Does anybody know what this PI means? To the naive reader (me), it looks
like some sort of stand-in for conref?

Robert D Anderson
IBM Authoring Tools Development
Chief Architect, DITA Open Toolkit