Add more information about the course file format.

Also add a reference to unit.eu's protocol OAI-PMH. Looks nice.

SPECIFICATIONS.md

 
+# THIS DOCUMENT IS A DRAFT
+
+> Contributions welcome!
+
 ## Courses Model
 
 Each Course MUST have:
@@ -14,7 +18,35 @@ Each course MAY have
 - one or more Courses as dependencies
 - one or more Tags
 
+Keep it simple, for now.  There will be room for events (class projects, etc.) later.
+
+## Course File Format
+
+We should probably follow something akin to [what Grav does](https://learn.getgrav.org/15/content/content-pages).
+
+- A frontmatter in YAML holding metadata
+- The course in Markdown + HTML
+
+The markdown enhancements should be documented here as well.
+
+Ideas:
+- use gitlab's flavor as base, since it has latex and mermaid already
+- https://zestedesavoir.com/ has a pretty good markdown flavor as well (information and warning bubbles), tailored for education
+
+## Possible driver implementations
+
+- with Grav
+- with Moodle
+- with schema.org (jsonld?) (may use Grav for this)
+- with OAI-PMH  (may use Grav for this?)
+
+Multiple frontends may be buit to display these courses.
+
+## Tips
+
+http://flagpedia.net/emoji
 
 ## TODO
 
-- Look up https://schema.org/Course and comply somehow
\ No newline at end of file
+- Look up https://schema.org/Course and comply somehow
+- Look up [OAI-PMH](ttp://www.unit.eu/ressources-educatives-libres/valoriser-des-rel) and comply somehow