doc,tools: use only one level 1 header per page

Increment the header levels from markdown files when producing HTML
documents. This is both better semantically (as the two h1 headers in
current docs are not actually equivalent level semantically--the second
belongs below/inside the first) and better for accessibility. (It is
valid HTML to have multiple h1 headers in a document, but it can be bad
for screen reader experience.)

PR-URL: #37839
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Pooja D P <Pooja.D.P@ibm.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: Trott

test/doctool/test-doctool-html.js

@@ -60,25 +60,25 @@ function toHTML({ input, filename, nodeVersion, versions }) {
 const testData = [
   {
     file: fixtures.path('order_of_end_tags_5873.md'),
-    html: '<h3>Static method: Buffer.from(array) <span> ' +
+    html: '<h4>Static method: Buffer.from(array) <span> ' +
       '<a class="mark" href="#foo_static_method_buffer_from_array" ' +
-      'id="foo_static_method_buffer_from_array">#</a> </span> </h3>' +
+      'id="foo_static_method_buffer_from_array">#</a> </span> </h4>' +
       '<ul><li><code>array</code><a ' +
       'href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/' +
       'Reference/Global_Objects/Array" class="type">&#x3C;Array></a></li></ul>'
   },
   {
     file: fixtures.path('doc_with_yaml.md'),
-    html: '<h1>Sample Markdown with YAML info' +
+    html: '<h2>Sample Markdown with YAML info' +
       '<span><a class="mark" href="#foo_sample_markdown_with_yaml_info" ' +
-      ' id="foo_sample_markdown_with_yaml_info">#</a></span></h1>' +
-      '<section><h2>Foobar<span><a class="mark" href="#foo_foobar" ' +
-      'id="foo_foobar">#</a></span></h2>' +
+      ' id="foo_sample_markdown_with_yaml_info">#</a></span></h2>' +
+      '<section><h3>Foobar<span><a class="mark" href="#foo_foobar" ' +
+      'id="foo_foobar">#</a></span></h3>' +
       '<div class="api_metadata"><span>Added in: v1.0.0</span></div> ' +
       '<p>Describe <code>Foobar</code> in more detail here.</p>' +
       '</section><section>' +
-      '<h2>Foobar II<span><a class="mark" href="#foo_foobar_ii" ' +
-      'id="foo_foobar_ii">#</a></span></h2><div class="api_metadata">' +
+      '<h3>Foobar II<span><a class="mark" href="#foo_foobar_ii" ' +
+      'id="foo_foobar_ii">#</a></span></h3><div class="api_metadata">' +
       '<details class="changelog"><summary>History</summary>' +
       '<table><tbody><tr><th>Version</th><th>Changes</th></tr>' +
       '<tr><td>v5.3.0, v4.2.0</td>' +
@@ -88,15 +88,15 @@ const testData = [
       '<p>Describe <code>Foobar II</code> in more detail here.' +
       '<a href="http://man7.org/linux/man-pages/man1/fg.1.html"><code>fg(1)' +
       '</code></a></p></section><section>' +
-      '<h2>Deprecated thingy<span><a class="mark" ' +
+      '<h3>Deprecated thingy<span><a class="mark" ' +
       'href="#foo_deprecated_thingy" id="foo_deprecated_thingy">#</a>' +
-      '</span></h2><div class="api_metadata"><span>Added in: v1.0.0</span>' +
+      '</span></h3><div class="api_metadata"><span>Added in: v1.0.0</span>' +
       '<span>Deprecated since: v2.0.0</span></div><p>Describe ' +
       '<code>Deprecated thingy</code> in more detail here.' +
       '<a href="http://man7.org/linux/man-pages/man1/fg.1p.html"><code>fg(1p)' +
       '</code></a></p></section><section>' +
-      '<h2>Something<span><a class="mark" href="#foo_something' +
-      '" id="foo_something">#</a></span></h2> ' +
+      '<h3>Something<span><a class="mark" href="#foo_something' +
+      '" id="foo_something">#</a></span></h3> ' +
       '<!-- This is not a metadata comment --> ' +
       '<p>Describe <code>Something</code> in more detail here. </p></section>'
   },
@@ -111,19 +111,19 @@ const testData = [
   },
   {
     file: fixtures.path('document_with_links.md'),
-    html: '<h1>Usage and Example<span><a class="mark"' +
+    html: '<h2>Usage and Example<span><a class="mark"' +
     'href="#foo_usage_and_example" id="foo_usage_and_example">#</a>' +
-    '</span></h1><section><h2>Usage<span><a class="mark" href="#foo_usage"' +
-    'id="foo_usage">#</a></span></h2><p><code>node \\[options\\] index.js' +
+    '</span></h2><section><h3>Usage<span><a class="mark" href="#foo_usage"' +
+    'id="foo_usage">#</a></span></h3><p><code>node \\[options\\] index.js' +
     '</code></p><p>Please see the<a href="cli.html#cli-options">' +
     'Command Line Options</a>document for more information.</p>' +
-    '</section><section><h2>' +
+    '</section><section><h3>' +
     'Example<span><a class="mark" href="#foo_example" id="foo_example">' +
-    '#</a></span></h2><p>An example of a<a href="example.html">' +
+    '#</a></span></h3><p>An example of a<a href="example.html">' +
     'webserver</a>written with Node.js which responds with<code>' +
     '\'Hello, World!\'</code>:</p></section><section>' +
-    '<h2>See also<span><a class="mark"' +
-    'href="#foo_see_also" id="foo_see_also">#</a></span></h2><p>Check' +
+    '<h3>See also<span><a class="mark"' +
+    'href="#foo_see_also" id="foo_see_also">#</a></span></h3><p>Check' +
     'out also<a href="https://nodejs.org/">this guide</a></p></section>'
   },
   {

tools/doc/html.js

@@ -66,10 +66,19 @@ const gtocHTML = unified()
 const templatePath = path.join(docPath, 'template.html');
 const template = fs.readFileSync(templatePath, 'utf8');
 
-function wrapSections(content) {
+function processContent(content) {
+  content = content.toString();
+  // Increment header tag levels to avoid multiple h1 tags in a doc.
+  // This means we can't already have an <h6>.
+  if (content.includes('<h6>')) {
+    throw new Error('Cannot increment a level 6 header');
+  }
+  // `++level` to convert the string to a number and increment it.
+  content = content.replace(/(?<=<\/?h)[1-5](?=[^<>]*>)/g, (level) => ++level);
+  // Wrap h3 tags in section tags.
   let firstTime = true;
-  return content.toString()
-    .replace(/<h2/g, (heading) => {
+  return content
+    .replace(/<h3/g, (heading) => {
       if (firstTime) {
         firstTime = false;
         return '<section>' + heading;
@@ -91,7 +100,7 @@ function toHTML({ input, content, filename, nodeVersion, versions }) {
                      .replace('__GTOC__', gtocHTML.replace(
                        `class="nav-${id}"`, `class="nav-${id} active"`))
                      .replace('__EDIT_ON_GITHUB__', editOnGitHub(filename))
-                     .replace('__CONTENT__', wrapSections(content));
+                     .replace('__CONTENT__', processContent(content));
 
   const docCreated = input.match(
     /<!--\s*introduced_in\s*=\s*v([0-9]+)\.([0-9]+)\.[0-9]+\s*-->/);