feat: logical structure of lesson

CONTRIBUTING.md

@@ -43,7 +43,32 @@ All contributors will be acknowledged.
  solid 1-point black lines,
  and unfilled objects.
 
-## Repository Contents
+## Logical Structure
+
+- Introduction
+ - A *learner persona* that characterizes the intended audience in concrete terms.
+ - *Prerequisites* (which should be interpreted with reference to the learner persona).
+ - *Learning objectives* that define the tutorial's scope.
+ - *Setup instructions* that instructors and learners must go through in order to code along
+- Episodes
+ - *Runnable episodes* are numbered.
+ Each contains one code sample, its output, and notes for the instructor.
+ Learners are *not* expected to be able to understand episodes without instructor elaboration.
+ - *Asides* are not numbered,
+ and contain code-less explanatory material,
+ additional setup instructions,
+ *concept maps* summarizing recently-introduced ideas,
+ etc.
+ - Episodes of both kinds may contain *glossary references*
+ and/or *explanatory diagrams*.
+- Appendices
+ - A *glossary* that defines terms called out in the episodes.
+ - *Acknowledgments* that point at inspirations and thank contributors.
+- Links
+ - All external links are written using `{% raw %}[box][notation]{% endraw %}` inline
+ and defined at the foot of the document.
+
+## Physical Structure
 
 - `CODE_OF_CONDUCT.md`: source for Code of Conduct
  - `conduct_.md`: auxiliary file to translate CoC into HTML