Does anyone know if attributes get attached to headline elements during the
export process? I am writing a derived backend in which I would like to
have a line like

(let (add-toggle (org-export-read-attribute :attr_canvas_html headline
:toggle))
....)

But as var as i can tell, the call to org-rexport-read-attribute always
evaluates to nil in a file like this:

#+ATTR_CANVAS_HTML: :toggle t
* My TOggle Headline

Am I missing something obvious, or is htis not possible? I notice that none
of the org-xxx-headline functions in ox-xxx.el seem to check for
attributes, so maybe this is by design?

THanks,

Matt