[O] export subtree

[Skip Collins]

The export dispatcher allows me to export only the current subtree.
This is nice, but I would like to avoid having to put point in just
the right place before invoking the dispatcher. I have a document with
lots of things in it. One of the top-level headlines contains the
content of what I want to export. Is there a way to flag this heading
and its contents as the main export document so that wherever my
cursor is, when I export the document it only processes the correct
heading, treating its text as the title of the document?