From 4420913049f18492aa7a68a9da5d31983707d887 Mon Sep 17 00:00:00 2001
From: Elian Doran <contact@eliandoran.me>
Date: Sun, 27 Jul 2025 12:16:42 +0300
Subject: [PATCH] fix(export/markdown): superscript and subscript not preserved
 (closes #4307)

---
 apps/server/src/services/export/markdown.spec.ts | 6 ++++++
 apps/server/src/services/export/markdown.ts      | 2 +-
 apps/server/src/services/import/markdown.spec.ts | 6 ++++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/apps/server/src/services/export/markdown.spec.ts b/apps/server/src/services/export/markdown.spec.ts
index ac9d2aa04..fe1dc1c37 100644
--- a/apps/server/src/services/export/markdown.spec.ts
+++ b/apps/server/src/services/export/markdown.spec.ts
@@ -378,4 +378,10 @@ describe("Markdown export", () => {
         expect(markdownExportService.toMarkdown(html)).toBe(expected);
     });
 
+    it("preserves superscript and subscript", () => {
+        const html = /*html*/`<p>Hello <sup><strong>superscript</strong></sup> <sub><strong>subscript</strong></sub></p>`;
+        const expected = `Hello <sup><strong>superscript</strong></sup> <sub><strong>subscript</strong></sub>`;
+        expect(markdownExportService.toMarkdown(html)).toBe(expected);
+    });
+
 });
diff --git a/apps/server/src/services/export/markdown.ts b/apps/server/src/services/export/markdown.ts
index 6bbaf386d..ed16c6b30 100644
--- a/apps/server/src/services/export/markdown.ts
+++ b/apps/server/src/services/export/markdown.ts
@@ -56,7 +56,7 @@ function toMarkdown(content: string) {
         instance.addRule("math", buildMathFilter());
         instance.addRule("li", buildListItemFilter());
         instance.use(gfm);
-        instance.keep([ "kbd" ]);
+        instance.keep([ "kbd", "sup", "sub" ]);
     }
 
     return instance.turndown(content);
diff --git a/apps/server/src/services/import/markdown.spec.ts b/apps/server/src/services/import/markdown.spec.ts
index c8d06e28e..0bf747a81 100644
--- a/apps/server/src/services/import/markdown.spec.ts
+++ b/apps/server/src/services/import/markdown.spec.ts
@@ -299,4 +299,10 @@ $$`;
         expect(markdownService.renderToHtml(input, "Title")).toStrictEqual(expected);
     });
 
+    it("preserves superscript and subscript", () => {
+        const input = `Hello <sup>superscript</sup> <sub>subscript</sub>`;
+        const expected = /*html*/`<p>Hello <sup>superscript</sup> <sub>subscript</sub></p>`;
+        expect(markdownService.renderToHtml(input, "Title")).toStrictEqual(expected);
+    });
+
 });