For agents: start with the agent guide. Every page is Markdown by default; add Accept: text/html for HTML.

mdsvex left unified

mdsvex compiles Markdown with Svelte components. unified processes documents through plugins. remark processes Markdown, and rehype processes HTML.¶

CommonMark specifies Markdown syntax. GitHub Flavored Markdown (GFM) adds features to that syntax.¶

In Discussion #259, pngwn gives four reasons to leave unified:¶

• Performance.¶
• API instability.¶
• Poor documentation.¶
• Possible changes to allowed syntax extensions.¶

The new parser uses its own plugin system instead of remark and rehype plugins.¶

Penguin-flavoured markdown, or PFM, also changes syntax. On Reddit, as evilpingwin, pngwn says GFM’s features remain supported. The syntax is not always identical. He promises an automated migration path.¶

Where we stopped

Our local check of published mdsvex@1.0.0-next.0 stops on this minimal CommonMark input:¶

- **`x`** x
- y

The published migrator converts it to PFM:¶

- *`x`* x
- y

PFM uses one asterisk for strong text; CommonMark uses two.¶

The next.0 check gives these results:¶

• The compiler prints Infinite loop detected.¶
• The second list item disappears.¶
• The parser reports zero errors.¶
• A supplied rehype plugin is never called.¶

These results cover the published 1.0.0-next.0 prerelease only. We keep 0.12.8. The fence³⁹ does not permit rewriting valid prose around a parser defect.¶

The migrator still uses remark

The published migrator depends on unified, remark-parse, and remark-gfm. The new renderer leaves that ecosystem. The migration into it still reads CommonMark with remark.¶

Last changed 2026-10-07 in f1a00f2. Source on GitHub. Change log.