The short description and searching

In this sentence from the DITA 1.2 description of shortdesc

     The short description, which represents the purpose or theme of the
topic, is also intended to be used as a link preview and for
searching.

what does "for searching" mean?

I know that a <shortdesc> text is supposed to be the blurb that appears in
a search engine's results.  But the only way I can conceive of <shortdes>c
to "be used ... for searching" is that, when the topic is published as
HTML, the <shortdesc> text is output in the HTML <abstract> element
(unless a larger <abstract> is in the topic's metadata, in which case THAT
is used).

Is that what the "for searching" means?  What about other file types, such
as PDF?

--Thanks,
      Guy