docs(html-lang-require): add missing documentation

nschonni · nschonni · commit 8b9ddd334adb · 2021-12-24T21:21:55.000-05:00
diff --git a/docs/user-guide/list-rules.md b/docs/user-guide/list-rules.md
@@ -9,6 +9,7 @@ title: List of rules
 
 - [`doctype-first`](/docs/user-guide/rules/doctype-first): Doctype must be declared first.
 - [`doctype-html5`](/docs/user-guide/rules/doctype-html5): Invalid doctype.
+- [`html-lang-require`](/docs/user-guide/rules/html-lang-require): The HTML lang attribute is required.
 - [`head-script-disabled`](/docs/user-guide/rules/head-script-disabled): The `<script>` tag cannot be used in a tag.
 - [`style-disabled`](/docs/user-guide/rules/style-disabled): `<style>` tags cannot be used.
 - [`title-require`](/docs/user-guide/rules/title-require): `<title>` must be present in `<head>` tag.
diff --git a/docs/user-guide/rules/html-lang-require.md b/docs/user-guide/rules/html-lang-require.md
@@ -0,0 +1,42 @@
+---
+id: html-lang-require
+title: html-lang-require
+keywords:
+  - i18n
+---
+
+The lang attribute of an `<html>` element must be present and should be valid.
+
+Level: warning
+
+## Config value
+
+1. true: enable rule
+2. false: disable rule
+
+The following pattern are **not** considered rule violations:
+
+<!-- prettier-ignore -->
+```html
+<html lang="en"></html>
+```
+
+The following patterns are considered a rule violations:
+
+<!-- prettier-ignore -->
+```html
+<!-- missing lang tag -->
+<html></html>
+```
+
+<!-- prettier-ignore -->
+```html
+<!-- empty lang tag -->
+<html lang=""></html>
+```
+
+<!-- prettier-ignore -->
+```html
+<!-- invalid BCP 47 lang value -->
+<html lang="-"></html>
+```
