Summary
This postmortem analyzes why syntax‑highlighted R/Python code produced by exams2html() loses all color when exported to Moodle XML via exams2moodle(). The issue stems from Moodle’s limited support for HTML/CSS in question text and the way the r‑exams package sanitizes output for LMS compatibility.
Root Cause
- Moodle’s XML format strips or ignores CSS classes used for syntax highlighting.
exams2moodle()intentionally removes inline styles to avoid Moodle rejecting the question.- Moodle’s built‑in code formatting uses plain
<pre>blocks without highlighting. - The r‑exams pipeline does not embed external CSS or JS, which Moodle would not load anyway.
Why This Happens in Real Systems
- LMS platforms often sanitize HTML aggressively to prevent security issues.
- External CSS/JS is typically blocked in question text.
- Syntax highlighting libraries (e.g., highlight.js, prism.js) require scripts Moodle does not execute.
- Exporters like r‑exams must target the lowest common denominator to ensure imports do not fail.
Real-World Impact
- Students see uncolored, harder‑to‑read code in Moodle quizzes.
- Instructors lose pedagogical clarity when teaching programming concepts.
- Debugging or comprehension questions become more error‑prone.
- Courses relying on code literacy experience reduced exam usability.
Example or Code (if necessary and relevant)
Below is a minimal example of what Moodle receives—note the absence of styling:
x <- 1:10
mean(x)How Senior Engineers Fix It
Senior engineers typically apply one of these strategies:
- Use Moodle’s built‑in syntax highlighter by wrapping code in:
```{.language-r}(if the theme supports it)
- Enable the Moodle “Syntax Highlighting” filter (requires admin rights).
- Switch to the STACK or CodeRunner question types, which support proper highlighting.
- Embed code as an image when formatting fidelity is critical.
- Patch r‑exams templates to inject Moodle‑compatible
<pre class="prettyprint">blocks (works only if the Moodle theme loads Google Prettify).
Why Juniors Miss It
- They assume HTML rendering is consistent across platforms, which is rarely true.
- They expect LMS systems to behave like modern browsers, but Moodle sanitizes heavily.
- They do not realize that r‑exams exporters intentionally strip styling for compatibility.
- They overlook that syntax highlighting requires JavaScript, which Moodle question text does not execute.