Merge pull request #12455 from quarto-dev/fix/embed-doctype

don't loose DOCTYPE header in embed resource processing

Author: cscheid

src/core/pandoc/self-contained.ts

@@ -48,11 +48,15 @@ export const pandocIngestSelfContainedContent = async (
 
   // The raw html contents
   const contents = Deno.readTextFileSync(file);
+  const doctypeMatch = contents.match(/^<!DOCTYPE.*?>/);
   const dom = await parseHtml(contents);
   await bundleModules(dom, workingDir);
 
   const input: string[] = [];
   input.push("````````{=html}");
+  if (doctypeMatch) {
+    input.push(doctypeMatch[0]);
+  }
   input.push(dom.documentElement!.outerHTML);
   input.push("````````");
 

tests/docs/smoke-all/2025/04/04/12295.qmd

@@ -0,0 +1,28 @@
+---
+title: DOCTYPE is not lost when using embed-resources
+embed-resources: true
+_quarto:
+  tests:
+    html:
+      ensureHtmlElements:
+        - []
+        - []
+      ensureFileRegexMatches:
+        - ['\<\!DOCTYPE html\>'] 
+        - []
+    revealjs:
+      ensureHtmlElements:
+        - []
+        - []
+      ensureFileRegexMatches:
+        - ['\<\!DOCTYPE html\>'] 
+        - []
+---
+
+Example from https://github.com/quarto-dev/quarto-cli/issues/12295: Not having DOCTYPE lead to browser using a Quirk mode for CSS, and not applying the standard HTML5. 
+
+## Header
+
+```bash
+quarto render --help
+```