From e515629a1e5bc9a00733d00fc7d3d8042d80bcf1 Mon Sep 17 00:00:00 2001
From: Christophe Dervieux <christophe.dervieux@gmail.com>
Date: Mon, 16 Feb 2026 16:57:57 +0100
Subject: [PATCH 1/2] Fix multi-line subtitle escaping its CSS class in HTML
 output

Convert MetaBlocks to MetaInlines for subtitle field in normalize.lua,
preventing nested <p> tags (invalid HTML5) when YAML uses literal block
scalar (|).

Fixes #13827

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/resources/filters/normalize/normalize.lua | 14 +++++++++++-
 .../docs/smoke-all/2026/02/16/issue-13827.qmd | 22 +++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 tests/docs/smoke-all/2026/02/16/issue-13827.qmd

diff --git a/src/resources/filters/normalize/normalize.lua b/src/resources/filters/normalize/normalize.lua
index 121b571ddc7..08439f53f21 100644
--- a/src/resources/filters/normalize/normalize.lua
+++ b/src/resources/filters/normalize/normalize.lua
@@ -20,7 +20,16 @@ local authors = require 'modules/authors'
 local license = require 'modules/license'
 local shortcode_ast = require 'modules/astshortcode'
 
-function normalize_filter() 
+-- Convert block-level metadata to inline for fields rendered inside <p> tags.
+-- Multi-line YAML values produce MetaBlocks (Para), which nest <p> in <p> — invalid HTML5.
+local function ensureMetaInlines(meta, field)
+  local val = meta[field]
+  if val ~= nil and quarto.utils.type(val) == "Blocks" then
+    meta[field] = quarto.utils.as_inlines(val)
+  end
+end
+
+function normalize_filter()
   return {
     Meta = function(meta)
       -- normalizes the author/affiliation metadata
@@ -32,6 +41,9 @@ function normalize_filter()
       -- normalizes the license metadata
       normalized = license.processLicenseMeta(normalized)
 
+      -- Convert block-level metadata to inline for fields rendered in <p> tags
+      ensureMetaInlines(normalized, "subtitle")
+
       -- for JATs, forward keywords or categories to tags
       if _quarto.format.isJatsOutput() then
         if normalized.tags == nil then
diff --git a/tests/docs/smoke-all/2026/02/16/issue-13827.qmd b/tests/docs/smoke-all/2026/02/16/issue-13827.qmd
new file mode 100644
index 00000000000..01d462d5bf5
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/16/issue-13827.qmd
@@ -0,0 +1,22 @@
+---
+title: Test Title
+subtitle: |
+  A Single Line Subtitle
+format:
+  html: default
+  revealjs: default
+_quarto:
+  tests:
+    html:
+      ensureHtmlElementContents:
+        selectors: ['p.subtitle']
+        matches: ['A Single Line Subtitle']
+    revealjs:
+      ensureHtmlElementContents:
+        selectors: ['p.subtitle']
+        matches: ['A Single Line Subtitle']
+---
+
+## Test Content
+
+This tests that a single-line | scalar subtitle stays inside the subtitle class.

From b87f64493af2e61dbc8e5318cd18d86bb0dca1fa Mon Sep 17 00:00:00 2001
From: Christophe Dervieux <christophe.dervieux@gmail.com>
Date: Mon, 16 Feb 2026 17:11:49 +0100
Subject: [PATCH 2/2] Add multi-paragraph subtitle test case for #13827

Exercises the MetaBlocks-with-multiple-Para path where
blocks_to_inlines joins paragraphs with LineBreak separators.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 .../2026/02/16/issue-13827-multiline.qmd      | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 tests/docs/smoke-all/2026/02/16/issue-13827-multiline.qmd

diff --git a/tests/docs/smoke-all/2026/02/16/issue-13827-multiline.qmd b/tests/docs/smoke-all/2026/02/16/issue-13827-multiline.qmd
new file mode 100644
index 00000000000..c6ca79c9f4d
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/16/issue-13827-multiline.qmd
@@ -0,0 +1,24 @@
+---
+title: Test Title
+subtitle: |
+  First Part
+
+  Second Part
+format:
+  html: default
+  revealjs: default
+_quarto:
+  tests:
+    html:
+      ensureHtmlElementContents:
+        selectors: ['p.subtitle']
+        matches: ['First Part']
+    revealjs:
+      ensureHtmlElementContents:
+        selectors: ['p.subtitle']
+        matches: ['First Part']
+---
+
+## Test Content
+
+This tests that a multi-paragraph | scalar subtitle stays inside the subtitle class.