Limits on fallback handling for unknown language hints in fenced code blocks

Fallback Recommendation

Renderers should treat an unknown language hint as plain text, preserving the info string but applying no syntax highlighting. This is the safest fallback because it keeps the original content intact and avoids misleading highlighting.

Confirmed Facts

The CommonMark and GFM specifications permit any info string in fenced code blocks but do not define a required fallback behavior. Consequently, each renderer decides independently, leading to divergent outcomes such as no highlighting, generic highlighting, or suppression.

Next Steps

1. Identify the specific Markdown processor and its version you will use.
2. Create a test fenced code block with an unknown language hint, e.g., ```unknown.
3. Render the block and inspect the resulting HTML to see whether highlighting is applied, the info string is retained, or the block is treated as plain text.
4. If the output deviates from plain‑text fallback, adjust the source (use a known language like text or none) or implement post‑processing to normalize the info string.

Which Markdown processor and its exact version are you targeting? This detail determines whether any version‑specific behavior might affect the recommendation.