From 198b27600f8afdd201c01b60c127e06c34de21ab Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Canouil?=
 <8896044+mcanouil@users.noreply.github.com>
Date: Sat, 17 Oct 2026 23:50:23 +0200
Subject: [PATCH 1/6] fix: load sibling modules without the debug library

q2 has no debug library, so every module that loads a sibling failed to load there, and an extension that used one stopped with a shortcode script error. Without debug, load_sibling now passes the bare name to require, which q2 resolves in the directory of the module being loaded. quarto-cli keeps the absolute path, because a bare require('string') there returns the standard library.
---
 modules/content-extraction.lua |  8 ++++-
 modules/html.lua               |  8 ++++-
 modules/metadata.lua           |  8 ++++-
 modules/pandoc-helpers.lua     |  8 ++++-
 modules/paths.lua              |  8 ++++-
 modules/schema-check.lua       |  8 ++++-
 tests/run.lua                  | 63 ++++++++++++++++++++++++++++++++++
 7 files changed, 105 insertions(+), 6 deletions(-)

diff --git a/modules/content-extraction.lua b/modules/content-extraction.lua
index fd7b55b..290e62b 100644
--- a/modules/content-extraction.lua
+++ b/modules/content-extraction.lua
@@ -10,9 +10,15 @@ local M = {}
 --- @param filename string The sibling module filename (e.g., 'string.lua')
 --- @return table The loaded module
 local function load_sibling(filename)
+  local name = filename:gsub('%.lua$', '')
+  if not debug then
+    -- q2 has no `debug` library, and its `require` looks in the directory of
+    -- the module being loaded first.
+    return require(name)
+  end
   local source = debug.getinfo(1, 'S').source:sub(2)
   local dir = source:match('(.*[/\\])') or ''
-  return require((dir .. filename):gsub('%.lua$', ''))
+  return require(dir .. name)
 end
 
 --- Load required modules
diff --git a/modules/html.lua b/modules/html.lua
index ecb4870..eba6b98 100644
--- a/modules/html.lua
+++ b/modules/html.lua
@@ -10,9 +10,15 @@ local M = {}
 --- @param filename string The sibling module filename (e.g., 'string.lua')
 --- @return table The loaded module
 local function load_sibling(filename)
+  local name = filename:gsub('%.lua$', '')
+  if not debug then
+    -- q2 has no `debug` library, and its `require` looks in the directory of
+    -- the module being loaded first.
+    return require(name)
+  end
   local source = debug.getinfo(1, 'S').source:sub(2)
   local dir = source:match('(.*[/\\])') or ''
-  return require((dir .. filename):gsub('%.lua$', ''))
+  return require(dir .. name)
 end
 
 --- Load string module for escape_html and escape_attribute
diff --git a/modules/metadata.lua b/modules/metadata.lua
index 7bc55c1..abe45a6 100644
--- a/modules/metadata.lua
+++ b/modules/metadata.lua
@@ -10,9 +10,15 @@ local M = {}
 --- @param filename string The sibling module filename (e.g., 'string.lua')
 --- @return table The loaded module
 local function load_sibling(filename)
+  local name = filename:gsub('%.lua$', '')
+  if not debug then
+    -- q2 has no `debug` library, and its `require` looks in the directory of
+    -- the module being loaded first.
+    return require(name)
+  end
   local source = debug.getinfo(1, 'S').source:sub(2)
   local dir = source:match('(.*[/\\])') or ''
-  return require((dir .. filename):gsub('%.lua$', ''))
+  return require(dir .. name)
 end
 
 --- Load required modules
diff --git a/modules/pandoc-helpers.lua b/modules/pandoc-helpers.lua
index f90919b..9525273 100644
--- a/modules/pandoc-helpers.lua
+++ b/modules/pandoc-helpers.lua
@@ -10,9 +10,15 @@ local M = {}
 --- @param filename string The sibling module filename (e.g., 'string.lua')
 --- @return table The loaded module
 local function load_sibling(filename)
+  local name = filename:gsub('%.lua$', '')
+  if not debug then
+    -- q2 has no `debug` library, and its `require` looks in the directory of
+    -- the module being loaded first.
+    return require(name)
+  end
   local source = debug.getinfo(1, 'S').source:sub(2)
   local dir = source:match('(.*[/\\])') or ''
-  return require((dir .. filename):gsub('%.lua$', ''))
+  return require(dir .. name)
 end
 
 --- Load string module for is_empty
diff --git a/modules/paths.lua b/modules/paths.lua
index e00670d..4407e82 100644
--- a/modules/paths.lua
+++ b/modules/paths.lua
@@ -10,9 +10,15 @@ local M = {}
 --- @param filename string The sibling module filename (e.g., 'string.lua')
 --- @return table The loaded module
 local function load_sibling(filename)
+  local name = filename:gsub('%.lua$', '')
+  if not debug then
+    -- q2 has no `debug` library, and its `require` looks in the directory of
+    -- the module being loaded first.
+    return require(name)
+  end
   local source = debug.getinfo(1, 'S').source:sub(2)
   local dir = source:match('(.*[/\\])') or ''
-  return require((dir .. filename):gsub('%.lua$', ''))
+  return require(dir .. name)
 end
 
 --- Load string module for is_empty
diff --git a/modules/schema-check.lua b/modules/schema-check.lua
index 9fe2c17..6a40f97 100644
--- a/modules/schema-check.lua
+++ b/modules/schema-check.lua
@@ -36,9 +36,15 @@ local M = {}
 --- @param filename string The sibling module filename (e.g., 'string.lua')
 --- @return table The loaded module
 local function load_sibling(filename)
+  local name = filename:gsub('%.lua$', '')
+  if not debug then
+    -- q2 has no `debug` library, and its `require` looks in the directory of
+    -- the module being loaded first.
+    return require(name)
+  end
   local source = debug.getinfo(1, 'S').source:sub(2)
   local dir = source:match('(.*[/\\])') or ''
-  return require((dir .. filename):gsub('%.lua$', ''))
+  return require(dir .. name)
 end
 
 --- Load required modules
diff --git a/tests/run.lua b/tests/run.lua
index 032ddd0..be0603f 100644
--- a/tests/run.lua
+++ b/tests/run.lua
@@ -109,6 +109,69 @@ for _, name in ipairs(names) do
   end
 end
 
+io.stdout:write('# loading from an extension\n')
+
+--- The modules as an extension vendors them, in a directory whose path has a
+--- space. A shortcode loads every module that has siblings and prints what
+--- each one returned. quarto-cli has the `debug` library and q2 does not, so
+--- each renders the project with its own way to find the siblings.
+do
+  local with_siblings = { 'content-extraction', 'html', 'metadata', 'pandoc-helpers', 'paths', 'schema-check' }
+  local function quote(text)
+    return "'" .. text:gsub("'", "'\\''") .. "'"
+  end
+  local function write(path, text)
+    local handle = assert(io.open(path, 'w'))
+    handle:write(text)
+    handle:close()
+  end
+  pandoc.system.with_temporary_directory('lua-modules', function(tmp)
+    local project = tmp .. '/with space'
+    local vendor = project .. '/_extensions/probe/_vendor/quarto-lua-modules'
+    pandoc.system.make_directory(vendor, true)
+    os.execute('cp ' .. quote(here .. 'modules') .. '/*.lua ' .. quote(vendor))
+    local lines = { 'local loaded = {}' }
+    for _, name in ipairs(with_siblings) do
+      lines[#lines + 1] = string.format(
+        "loaded[#loaded + 1] = '%s=' .. type(require(quarto.utils.resolve_path('_vendor/quarto-lua-modules/%s.lua'):gsub('%%.lua$', '')))",
+        name, name)
+    end
+    lines[#lines + 1] = "return { probe = function() return pandoc.Str(table.concat(loaded, ',')) end }"
+    write(project .. '/_extensions/probe/probe.lua', table.concat(lines, '\n') .. '\n')
+    write(project .. '/_extensions/probe/_extension.yml',
+      'title: Probe\nversion: 1.0.0\ncontributes:\n  shortcodes:\n    - probe.lua\n')
+    write(project .. '/_quarto.yml', 'project:\n  type: default\n')
+    write(project .. '/doc.qmd', '---\ntitle: Probe\nformat: html\n---\n\n{{< probe >}}\n')
+
+    local expected = {}
+    for _, name in ipairs(with_siblings) do
+      expected[#expected + 1] = name .. '=table'
+    end
+    expected = table.concat(expected, ',')
+
+    local function render(command)
+      os.remove(project .. '/doc.html')
+      os.execute('cd ' .. quote(project) .. ' && ' .. command .. ' render doc.qmd > /dev/null 2>&1')
+      local handle = io.open(project .. '/doc.html', 'r')
+      if not handle then
+        return ''
+      end
+      local html = handle:read('a')
+      handle:close()
+      return html
+    end
+
+    check(render('quarto'):find(expected, 1, true) ~= nil,
+      'quarto-cli loads every module and its siblings from a vendored path with a space')
+    if os.execute('q2 --version > /dev/null 2>&1') then
+      check(render('q2'):find(expected, 1, true) ~= nil,
+        'q2, which has no `debug` library, loads every module and its siblings from a vendored path with a space')
+    else
+      io.stdout:write('skip q2 loads every module: q2 is not on the PATH\n')
+    end
+  end)
+end
+
 io.stdout:write('# exports\n')
 
 --- Checked both ways. `EXPECTED` is hand-maintained on purpose, because these

From 21ec15a1c682e24db57547fa32e3f105fc32bef8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Canouil?=
 <8896044+mcanouil@users.noreply.github.com>
Date: Sat, 17 Oct 2026 23:51:21 +0200
Subject: [PATCH 2/6] test: render the loading check with each engine in one
 loop

---
 tests/run.lua | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/tests/run.lua b/tests/run.lua
index be0603f..220e36a 100644
--- a/tests/run.lua
+++ b/tests/run.lua
@@ -130,12 +130,14 @@ do
     local vendor = project .. '/_extensions/probe/_vendor/quarto-lua-modules'
     pandoc.system.make_directory(vendor, true)
     os.execute('cp ' .. quote(here .. 'modules') .. '/*.lua ' .. quote(vendor))
-    local lines = { 'local loaded = {}' }
+    local lines, expected = { 'local loaded = {}' }, {}
     for _, name in ipairs(with_siblings) do
       lines[#lines + 1] = string.format(
         "loaded[#loaded + 1] = '%s=' .. type(require(quarto.utils.resolve_path('_vendor/quarto-lua-modules/%s.lua'):gsub('%%.lua$', '')))",
         name, name)
+      expected[#expected + 1] = name .. '=table'
     end
+    expected = table.concat(expected, ',')
     lines[#lines + 1] = "return { probe = function() return pandoc.Str(table.concat(loaded, ',')) end }"
     write(project .. '/_extensions/probe/probe.lua', table.concat(lines, '\n') .. '\n')
     write(project .. '/_extensions/probe/_extension.yml',
@@ -143,12 +145,6 @@ do
     write(project .. '/_quarto.yml', 'project:\n  type: default\n')
     write(project .. '/doc.qmd', '---\ntitle: Probe\nformat: html\n---\n\n{{< probe >}}\n')
 
-    local expected = {}
-    for _, name in ipairs(with_siblings) do
-      expected[#expected + 1] = name .. '=table'
-    end
-    expected = table.concat(expected, ',')
-
     local function render(command)
       os.remove(project .. '/doc.html')
       os.execute('cd ' .. quote(project) .. ' && ' .. command .. ' render doc.qmd > /dev/null 2>&1')
@@ -161,13 +157,13 @@ do
       return html
     end
 
-    check(render('quarto'):find(expected, 1, true) ~= nil,
-      'quarto-cli loads every module and its siblings from a vendored path with a space')
-    if os.execute('q2 --version > /dev/null 2>&1') then
-      check(render('q2'):find(expected, 1, true) ~= nil,
-        'q2, which has no `debug` library, loads every module and its siblings from a vendored path with a space')
-    else
-      io.stdout:write('skip q2 loads every module: q2 is not on the PATH\n')
+    for _, engine in ipairs({ 'quarto', 'q2' }) do
+      local description = engine .. ' loads every module and its siblings from a vendored path with a space'
+      if os.execute(engine .. ' --version > /dev/null 2>&1') then
+        check(render(engine):find(expected, 1, true) ~= nil, description)
+      else
+        io.stdout:write('skip ', description, ': ', engine, ' is not on the PATH\n')
+      end
     end
   end)
 end

From 90d10093d4d2787118c6d9d1bf094e26c1fbc3da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Canouil?=
 <8896044+mcanouil@users.noreply.github.com>
Date: Sat, 17 Oct 2026 23:55:40 +0200
Subject: [PATCH 3/6] test: prove each engine binds the sibling string module

---
 modules/content-extraction.lua |  2 +-
 modules/html.lua               |  2 +-
 modules/metadata.lua           |  2 +-
 modules/pandoc-helpers.lua     |  2 +-
 modules/paths.lua              |  2 +-
 modules/schema-check.lua       |  2 +-
 tests/run.lua                  | 26 +++++++++++++++++++-------
 7 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/modules/content-extraction.lua b/modules/content-extraction.lua
index 290e62b..59f3554 100644
--- a/modules/content-extraction.lua
+++ b/modules/content-extraction.lua
@@ -11,7 +11,7 @@ local M = {}
 --- @return table The loaded module
 local function load_sibling(filename)
   local name = filename:gsub('%.lua$', '')
-  if not debug then
+  if not (debug and debug.getinfo) then
     -- q2 has no `debug` library, and its `require` looks in the directory of
     -- the module being loaded first.
     return require(name)
diff --git a/modules/html.lua b/modules/html.lua
index eba6b98..d947a3c 100644
--- a/modules/html.lua
+++ b/modules/html.lua
@@ -11,7 +11,7 @@ local M = {}
 --- @return table The loaded module
 local function load_sibling(filename)
   local name = filename:gsub('%.lua$', '')
-  if not debug then
+  if not (debug and debug.getinfo) then
     -- q2 has no `debug` library, and its `require` looks in the directory of
     -- the module being loaded first.
     return require(name)
diff --git a/modules/metadata.lua b/modules/metadata.lua
index abe45a6..79a3a6e 100644
--- a/modules/metadata.lua
+++ b/modules/metadata.lua
@@ -11,7 +11,7 @@ local M = {}
 --- @return table The loaded module
 local function load_sibling(filename)
   local name = filename:gsub('%.lua$', '')
-  if not debug then
+  if not (debug and debug.getinfo) then
     -- q2 has no `debug` library, and its `require` looks in the directory of
     -- the module being loaded first.
     return require(name)
diff --git a/modules/pandoc-helpers.lua b/modules/pandoc-helpers.lua
index 9525273..5213f8e 100644
--- a/modules/pandoc-helpers.lua
+++ b/modules/pandoc-helpers.lua
@@ -11,7 +11,7 @@ local M = {}
 --- @return table The loaded module
 local function load_sibling(filename)
   local name = filename:gsub('%.lua$', '')
-  if not debug then
+  if not (debug and debug.getinfo) then
     -- q2 has no `debug` library, and its `require` looks in the directory of
     -- the module being loaded first.
     return require(name)
diff --git a/modules/paths.lua b/modules/paths.lua
index 4407e82..3012c7b 100644
--- a/modules/paths.lua
+++ b/modules/paths.lua
@@ -11,7 +11,7 @@ local M = {}
 --- @return table The loaded module
 local function load_sibling(filename)
   local name = filename:gsub('%.lua$', '')
-  if not debug then
+  if not (debug and debug.getinfo) then
     -- q2 has no `debug` library, and its `require` looks in the directory of
     -- the module being loaded first.
     return require(name)
diff --git a/modules/schema-check.lua b/modules/schema-check.lua
index 6a40f97..f16da4e 100644
--- a/modules/schema-check.lua
+++ b/modules/schema-check.lua
@@ -37,7 +37,7 @@ local M = {}
 --- @return table The loaded module
 local function load_sibling(filename)
   local name = filename:gsub('%.lua$', '')
-  if not debug then
+  if not (debug and debug.getinfo) then
     -- q2 has no `debug` library, and its `require` looks in the directory of
     -- the module being loaded first.
     return require(name)
diff --git a/tests/run.lua b/tests/run.lua
index 220e36a..9d91805 100644
--- a/tests/run.lua
+++ b/tests/run.lua
@@ -137,6 +137,12 @@ do
         name, name)
       expected[#expected + 1] = name .. '=table'
     end
+    -- A sibling bound to the wrong table still loads, so one call goes through
+    -- `string.lua`, which the standard library of the same name cannot answer.
+    lines[#lines + 1] = "local html = require(quarto.utils.resolve_path('_vendor/quarto-lua-modules/html.lua'):gsub('%.lua$', ''))"
+    lines[#lines + 1] = "local ok, header = pcall(html.raw_header, 2, 'T', 'a&b')"
+    lines[#lines + 1] = "loaded[#loaded + 1] = 'escaped=' .. tostring(ok and header:find('a&amp;b', 1, true) ~= nil)"
+    expected[#expected + 1] = 'escaped=true'
     expected = table.concat(expected, ',')
     lines[#lines + 1] = "return { probe = function() return pandoc.Str(table.concat(loaded, ',')) end }"
     write(project .. '/_extensions/probe/probe.lua', table.concat(lines, '\n') .. '\n')
@@ -145,22 +151,28 @@ do
     write(project .. '/_quarto.yml', 'project:\n  type: default\n')
     write(project .. '/doc.qmd', '---\ntitle: Probe\nformat: html\n---\n\n{{< probe >}}\n')
 
-    local function render(command)
-      os.remove(project .. '/doc.html')
-      os.execute('cd ' .. quote(project) .. ' && ' .. command .. ' render doc.qmd > /dev/null 2>&1')
-      local handle = io.open(project .. '/doc.html', 'r')
+    local function read(path)
+      local handle = io.open(path, 'r')
       if not handle then
         return ''
       end
-      local html = handle:read('a')
+      local text = handle:read('a')
       handle:close()
-      return html
+      return text
+    end
+
+    --- The rendered page, and the engine's output for the failure detail.
+    local function render(command)
+      os.remove(project .. '/doc.html')
+      os.execute('cd ' .. quote(project) .. ' && ' .. command .. ' render doc.qmd > render.log 2>&1')
+      return read(project .. '/doc.html'), read(project .. '/render.log')
     end
 
     for _, engine in ipairs({ 'quarto', 'q2' }) do
       local description = engine .. ' loads every module and its siblings from a vendored path with a space'
       if os.execute(engine .. ' --version > /dev/null 2>&1') then
-        check(render(engine):find(expected, 1, true) ~= nil, description)
+        local page, output = render(engine)
+        check(page:find(expected, 1, true) ~= nil, description, output:sub(-600))
       else
         io.stdout:write('skip ', description, ': ', engine, ' is not on the PATH\n')
       end

From baae6c03839e9df356683850aaa3deeb39ab69e0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Canouil?=
 <8896044+mcanouil@users.noreply.github.com>
Date: Sat, 17 Oct 2026 23:59:30 +0200
Subject: [PATCH 4/6] ci: run the loading check with q2

---
 .github/workflows/test.yml | 18 ++++++++++++++++++
 tests/run.lua              | 11 ++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2332f0e..6cd2d3e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -44,6 +44,24 @@ jobs:
       - name: Setup Quarto
         uses: quarto-dev/quarto-actions/setup@v2
 
+      # q2 has no `debug` library, so the modules find their siblings another
+      # way there. The suite renders a vendored copy with q2 when it is on the
+      # PATH, which this step provides. HTML needs no pandoc of its own.
+      - name: Set up q2
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
+          q2_dir="${RUNNER_TEMP}/q2"
+          mkdir -p -- "${q2_dir}/bin"
+          gh release download -R quarto-dev/q2 \
+            -p 'q2-*-linux_amd64.tar.gz' -p 'checksums.sha256' -D "${q2_dir}"
+          cd -- "${q2_dir}"
+          sha256sum --check --ignore-missing --strict checksums.sha256
+          tar -xzf q2-*-linux_amd64.tar.gz -C "${q2_dir}/bin"
+          printf '%s\n' "${q2_dir}/bin" >> "${GITHUB_PATH}"
+          "${q2_dir}/bin/q2" --version
+
       # The suite loads and executes every module it finds on disk, which
       # subsumes a parse check, so there is no separate one.
       - name: Run the tests
diff --git a/tests/run.lua b/tests/run.lua
index 9d91805..735c5c1 100644
--- a/tests/run.lua
+++ b/tests/run.lua
@@ -116,7 +116,16 @@ io.stdout:write('# loading from an extension\n')
 --- each one returned. quarto-cli has the `debug` library and q2 does not, so
 --- each renders the project with its own way to find the siblings.
 do
-  local with_siblings = { 'content-extraction', 'html', 'metadata', 'pandoc-helpers', 'paths', 'schema-check' }
+  -- Read from disk, so a module that starts to load a sibling is probed too.
+  local with_siblings = {}
+  for _, name in ipairs(names) do
+    local handle = assert(io.open(here .. 'modules/' .. name .. '.lua', 'r'))
+    if handle:read('a'):find('load_sibling(', 1, true) then
+      with_siblings[#with_siblings + 1] = name
+    end
+    handle:close()
+  end
+  check(#with_siblings == 6, 'six modules load a sibling', table.concat(with_siblings, ', '))
   local function quote(text)
     return "'" .. text:gsub("'", "'\\''") .. "'"
   end

From 304664c6c05c57705b3a1b619af4a0d9bc0edc4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Canouil?=
 <8896044+mcanouil@users.noreply.github.com>
Date: Sun, 18 Oct 2026 19:08:24 +0200
Subject: [PATCH 5/6] ci: pin the q2 release of the loading check

---
 .github/workflows/test.yml | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 6cd2d3e..97ecea0 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -46,7 +46,8 @@ jobs:
 
       # q2 has no `debug` library, so the modules find their siblings another
       # way there. The suite renders a vendored copy with q2 when it is on the
-      # PATH, which this step provides. HTML needs no pandoc of its own.
+      # PATH, which this step provides. HTML needs no pandoc of its own. The
+      # release is pinned, so a new q2 changes the job only through a commit.
       - name: Set up q2
         env:
           GH_TOKEN: ${{ github.token }}
@@ -54,7 +55,7 @@ jobs:
           set -euo pipefail
           q2_dir="${RUNNER_TEMP}/q2"
           mkdir -p -- "${q2_dir}/bin"
-          gh release download -R quarto-dev/q2 \
+          gh release download v0.34.0 -R quarto-dev/q2 \
             -p 'q2-*-linux_amd64.tar.gz' -p 'checksums.sha256' -D "${q2_dir}"
           cd -- "${q2_dir}"
           sha256sum --check --ignore-missing --strict checksums.sha256

From 84b64fce445698b0c0b03195ce5c27e4e75511cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Canouil?=
 <8896044+mcanouil@users.noreply.github.com>
Date: Sun, 18 Oct 2026 19:08:56 +0200
Subject: [PATCH 6/6] docs: add changelog entry for sibling loading on q2

---
 CHANGELOG.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b86fa0f..63a33b3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- fix: Load sibling modules on q2, which has no `debug` library. An extension that vendors the modules no longer stops there with a shortcode script error. (#12)
+
 ## 2.5.0 (2026-09-12)
 
 - feat: Add `Checker:format`, which checks one output format's options against the `formats` section and returns what they resolve to. It needs Quarto Wizard 3.6.0 or newer, whose `validate_format` reads the top level of the metadata where Quarto puts them.