✨ feat: add frontmatter extraction examples and documentation

Closes #1359

Author: harehare

README.md

@@ -329,6 +329,9 @@ mq 'select(.h1 || .h2)' example.html
 
 # Extract specific cell from a Markdown table
 mq '.[1][2] | to_text()' data.md
+
+# Extract frontmatter metadata from markdown files:
+import "yaml" | if (.yaml): yaml::yaml_parse() | get(:title)
 ```
 
 ### Using with markitdown

docs/books/src/start/example.md

@@ -461,3 +461,13 @@ $ mq -A 'let headers = count_by(fn(x): x | select(.h);)
 | let anchor = downcase(replace(text, " ", "-"))
 | if (!is_empty(text)): s"${indent}- [${text}](#${anchor})"
 ```
+
+## Frontmatter Operations
+
+Extract frontmatter metadata from markdown files:
+
+```mq
+import "yaml" | if (.yaml): yaml::yaml_parse() | get(:title)
+```
+
+

editors/vscode/src/extension.ts

@@ -39,6 +39,9 @@ def snake_to_camel(x):
 
 # CSV parse
 include "csv" | csv_parse("a,b,c\n1,2,3\n4,5,6", true) | csv_to_markdown_table()
+
+# Extract Front Matter
+import "yaml" | if (.yaml): yaml::yaml_parse() | get(:title)
 `;
 
 let client: lc.LanguageClient | null = null;

packages/mq-playground/src/examples.ts

@@ -254,6 +254,23 @@ end
 - [Chapter2](Chapter2.md)
   - [Chapter3](Chapter3.md)
 - [Chapter4](Chapter4.md)
+`,
+        isUpdate: false,
+        format: "markdown",
+      },
+      {
+        name: "Extract frontmatter data",
+        code: `import "yaml" | if (.yaml): yaml::yaml_parse() | get(:title)`,
+        markdown: `---
+title: "Sample Document"
+author: "John Doe"
+date: "2024-01-01"
+---
+
+# Sample Document
+
+This is a sample document with frontmatter.
+
 `,
         isUpdate: false,
         format: "markdown",