docs(Lowercase): Add Lowercase documentation

docs/ko/reference/built-in/Lowercase.md

@@ -1 +1,42 @@
-# Lowercase
+# Lowercase\<StringType>
+
+:::info
+`Capitalize\<StringType>`은 TypeScript 4.1 이상에서 사용할 수 있는 내장 유틸리티 타입이에요. 자세한 내용은 [타입스크립트 핸드북](https://www.typescriptlang.org/docs/handbook/2/template-literal-types.html#lowercasestringtype)과 [릴리즈 노트](https://devblogs.microsoft.com/typescript/announcing-typescript-4-1/)를 참고해주세요.
+:::
+
+## 개요
+
+`Lowercase<StringType>` 유틸리티 타입은 문자열의 각 문자를 소문자로 변환해요.
+
+## 문법
+
+```ts
+type Lowercase<S extends string> = intrinsic;
+```
+
+- **StringType (S)**: The string that you want to convert each character in the string to the lowercase version.
+
+## Examples
+
+#### Example #1
+
+```ts
+type Greeting = 'Hello, world';
+type QuietGreeting = Lowercase<Greeting>; // 'hello, world'
+
+type ASCIICacheKey<Str extends string> = `id-${Lowercase<Str>}`;
+type MainID = ASCIICacheKey<'MY_APP'>; // 'id-my_app'
+```
+
+#### Example #2
+
+```ts
+type Environment = 'DATABASE_URL' | 'NODE_ENV' | 'PORT';
+type LowercaseEnvironment = Lowercase<Environment>;
+
+const env: Record<LowercaseEnvironment, string> = {
+  database_url: 'mongodb://localhost:27017/db',
+  node_env: 'development',
+  port: '8000',
+};
+```

docs/reference/built-in/Lowercase.md

@@ -1 +1,42 @@
-# Lowercase
+# Lowercase\<StringType>
+
+:::info
+The `Lowercase<StringType>` utility type is available starting from TypeScript version 4.1. For more information see in [TypeScript Handbook](https://www.typescriptlang.org/docs/handbook/2/template-literal-types.html#lowercasestringtype), [Release Note](https://devblogs.microsoft.com/typescript/announcing-typescript-4-1/)
+:::
+
+## Overview
+
+The `Lowercase<StringType>` utility type in TypeScript is used to convert each character in the string to the lowercase version.
+
+## Syntax
+
+```ts
+type Lowercase<S extends string> = intrinsic;
+```
+
+- **StringType (S)**: The string that you want to convert each character in the string to the lowercase version.
+
+## Examples
+
+#### Example #1
+
+```ts
+type Greeting = 'Hello, world';
+type QuietGreeting = Lowercase<Greeting>; // 'hello, world'
+
+type ASCIICacheKey<Str extends string> = `id-${Lowercase<Str>}`;
+type MainID = ASCIICacheKey<'MY_APP'>; // 'id-my_app'
+```
+
+#### Example #2
+
+```ts
+type Environment = 'DATABASE_URL' | 'NODE_ENV' | 'PORT';
+type LowercaseEnvironment = Lowercase<Environment>;
+
+const env: Record<LowercaseEnvironment, string> = {
+  database_url: 'mongodb://localhost:27017/db',
+  node_env: 'development',
+  port: '8000',
+};
+```