I am writing this interface to my university's learning management system:
https://github.com/titaniumbones/Org-Marking-Mode/tree/use-structured-course-def.
I am only using hte exporting system tangentially and I have not defined a
new exporter. However, I would really like to be able to set some variable
values in the header section of hte document, e.g.:

#+ORG_LMS_COURSE: becomingmodern

or

#+PROPERTY: org-lms-course hackinghistory

I thought the latter might work but (org-entry-get-with-inheritance
"org-lms-course) and (org-entry-get-with-inheritance "ORG_LMS_COURSE") both
return nil.  The former is in any case somewhat cleaner-looking but I am
not finding in the manual an instructions on how to add my own keywords.
Is it possible to do this? I can of course always set a buffer-local
variable in a src block, e.g.:
#+begin_src emacs-lisp
(setq org-lms-course 'becomingmodern)
#+end_src.

but I would like to be able to avoid that where possible.

Thanks for the help as usual!