feat: update no-multiple-h1 rule to recognize JSON frontmatter

docs/rules/no-multiple-h1.md

@@ -10,9 +10,9 @@ An H1 heading is meant to define the main heading of a page, providing important
 
 This rule warns when it finds more than one H1 heading in a Markdown document. It checks for:
 
-- ATX-style headings (`# Heading`)
+- ATX-style headings (`# Heading` or `# Heading #`)
 - Setext-style headings (`Heading\n=========`)
-- Front matter title fields (YAML and TOML)
+- Front matter title fields ([YAML](https://yaml.org/), [TOML](https://toml.io/en/), and [JSON](https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Scripting/JSON))
 - HTML h1 tags (`<h1>Heading</h1>`)
 
 Examples of **incorrect** code for this rule:
@@ -46,7 +46,7 @@ Another H1 heading
 
 The following options are available on this rule:
 
-* `frontmatterTitle: string` - A regex pattern to match title fields in front matter. The default pattern matches both YAML (`title:`) and TOML (`title =`) formats. Set to an empty string to disable front matter title checking.
+* `frontmatterTitle: string` - A regex pattern to match title fields in front matter. The default pattern matches both YAML (`title:`), TOML (`title =`), and JSON (`"title":`) formats. Set to an empty string to disable front matter title checking.
 
 Examples of **incorrect** code for this rule:
 
@@ -57,7 +57,27 @@ Examples of **incorrect** code for this rule:
 title: My Title
 ---
 
-# Heading 1
+# Heading 1 with YAML front matter
+```
+
+```markdown
+<!-- eslint markdown/no-multiple-h1: "error" -->
+
++++
+title = "My Title"
++++
+
+# Heading 1 with TOML front matter
+```
+
+```markdown
+<!-- eslint markdown/no-multiple-h1: "error" -->
+
+---
+{ "title": "My Title" }
+---
+
+# Heading 1 with JSON front matter
 ```
 
 Examples of **incorrect** code when configured as `"no-multiple-h1": ["error", { frontmatterTitle: "\\s*heading\\s*[:=]" }]`:

src/rules/no-multiple-h1.js

@@ -75,7 +75,10 @@ export default {
 		],
 
 		defaultOptions: [
-			{ frontmatterTitle: "^\\s*['\"]?title['\"]?\\s*[:=]" },
+			{
+				frontmatterTitle:
+					"^(?!\\s*['\"]title[:=]['\"])\\s*\\{?\\s*['\"]?title['\"]?\\s*[:=]",
+			},
 		],
 	},
 
@@ -98,6 +101,12 @@ export default {
 				}
 			},
 
+			json(node) {
+				if (frontmatterHasTitle(node.value, titlePattern)) {
+					h1Count++;
+				}
+			},
+
 			html(node) {
 				let match;
 				while ((match = h1TagPattern.exec(node.value)) !== null) {