Hi,

  I learned from ox-html.el that the "#+BEGIN_HTML #+END_HTML" block can be
associated with a function by the ":export-block" argument in
"org-export-define-backend". But it seems doesn't apply to the "#+HTML:"
block.

  Could someone tell me how to define a one-line export-block for specific
exporter, like "#+HTML: " does for ox-html.el?

Regards,
Yujie