diff --git a/lib/node_modules/@stdlib/string/base/capitalize/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/base/capitalize/docs/types/index.d.ts
index 0a53a3227c09..2e261a40d9d2 100644
--- a/lib/node_modules/@stdlib/string/base/capitalize/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/base/capitalize/docs/types/index.d.ts
@@ -18,6 +18,8 @@
 
 // TypeScript Version: 4.1
 
+type Capitalize<S extends string> = S extends `${infer F}${infer R}` ? `${Uppercase<F>}${R}` : S;
+
 /**
 * Capitalizes the first character in a string.
 *
@@ -40,7 +42,7 @@
 * var out = capitalize( 'Hidden Treasures' );
 * // returns 'Hidden Treasures'
 */
-declare function capitalize( str: string ): string;
+declare function capitalize<S extends string>( str: S ): Capitalize<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/base/capitalize/docs/types/test.ts b/lib/node_modules/@stdlib/string/base/capitalize/docs/types/test.ts
index 072215f8e6a7..8644f23a5b2b 100644
--- a/lib/node_modules/@stdlib/string/base/capitalize/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/base/capitalize/docs/types/test.ts
@@ -23,7 +23,11 @@ import capitalize = require( './index' );
 
 // The function returns a string...
 {
-	capitalize( 'abc' ); // $ExpectType string
+	capitalize( 'abc' ); // $ExpectType "Abc"
+	capitalize( 'beep boop' ); // $ExpectType "Beep boop"
+	capitalize( 'a' ); // $ExpectType "A"
+	capitalize( 'A' ); // $ExpectType "A"
+	capitalize( 'abc' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/base/lowercase/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/base/lowercase/docs/types/index.d.ts
index d06fef844d12..b73454a5f91f 100644
--- a/lib/node_modules/@stdlib/string/base/lowercase/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/base/lowercase/docs/types/index.d.ts
@@ -28,7 +28,7 @@
 * var str = lowercase( 'bEEp' );
 * // returns 'beep'
 */
-declare function lowercase( str: string ): string;
+declare function lowercase<S extends string>( str: S ): Lowercase<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/base/lowercase/docs/types/test.ts b/lib/node_modules/@stdlib/string/base/lowercase/docs/types/test.ts
index daa8c2454224..50fbe9a6a5be 100644
--- a/lib/node_modules/@stdlib/string/base/lowercase/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/base/lowercase/docs/types/test.ts
@@ -23,7 +23,9 @@ import lowercase = require( './index' );
 
 // The function returns a string...
 {
-	lowercase( 'abc' ); // $ExpectType string
+	lowercase( 'ABC' ); // $ExpectType "abc"
+	lowercase( 'Beep BOOP' ); // $ExpectType "beep boop"
+	lowercase( 'abc' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/index.d.ts
index 31bbdd810822..a7860f7e5e4f 100644
--- a/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/index.d.ts
@@ -18,6 +18,8 @@
 
 // TypeScript Version: 4.1
 
+type Uncapitalize<S extends string> = S extends `${infer F}${infer R}` ? `${Lowercase<F>}${R}` : S;
+
 /**
 * Uncapitalizes the first character of a string.
 *
@@ -40,7 +42,7 @@
 * var out = uncapitalize( 'Hidden Treasures' );
 * // returns 'hidden Treasures'
 */
-declare function uncapitalize( str: string ): string;
+declare function uncapitalize<S extends string>( str: S ): Uncapitalize<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/test.ts b/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/test.ts
index bb1a0d2ff48f..197c29a25668 100644
--- a/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/base/uncapitalize/docs/types/test.ts
@@ -23,7 +23,11 @@ import uncapitalize = require( './index' );
 
 // The function returns a string...
 {
-	uncapitalize( 'Last man standing' ); // $ExpectType string
+	uncapitalize( 'Last man standing' ); // $ExpectType "last man standing"
+	uncapitalize( 'Hello World!' ); // $ExpectType "hello World!"
+	uncapitalize( 'BeepBoop' ); // $ExpectType "beepBoop"
+	uncapitalize( 'A' ); // $ExpectType "a"
+	uncapitalize( 'foo' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/base/uppercase/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/base/uppercase/docs/types/index.d.ts
index 6c3eb612a14b..4341559f3827 100644
--- a/lib/node_modules/@stdlib/string/base/uppercase/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/base/uppercase/docs/types/index.d.ts
@@ -28,7 +28,7 @@
 * var str = uppercase( 'bEEp' );
 * // returns 'BEEP'
 */
-declare function uppercase( str: string ): string;
+declare function uppercase<S extends string>( str: S ): Uppercase<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/base/uppercase/docs/types/test.ts b/lib/node_modules/@stdlib/string/base/uppercase/docs/types/test.ts
index 9d3278894f31..beae3f0d85e6 100644
--- a/lib/node_modules/@stdlib/string/base/uppercase/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/base/uppercase/docs/types/test.ts
@@ -23,7 +23,11 @@ import uppercase = require( './index' );
 
 // The function returns a string...
 {
-	uppercase( 'Last man standing' ); // $ExpectType string
+	uppercase( 'Last man standing' ); // $ExpectType "LAST MAN STANDING"
+	uppercase( 'Hello World!' ); // $ExpectType "HELLO WORLD!"
+	uppercase( 'beep' ); // $ExpectType "BEEP"
+	uppercase( 'BOOP' ); // $ExpectType "BOOP"
+	uppercase( 'foo' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/capitalize/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/capitalize/docs/types/index.d.ts
index c559d18cbe2f..60c2849ff641 100644
--- a/lib/node_modules/@stdlib/string/capitalize/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/capitalize/docs/types/index.d.ts
@@ -18,6 +18,8 @@
 
 // TypeScript Version: 4.1
 
+type Capitalize<S extends string> = S extends `${infer F}${infer R}` ? `${Uppercase<F>}${R}` : S;
+
 /**
 * Capitalizes the first character in a string.
 *
@@ -40,7 +42,7 @@
 * var out = capitalize( 'Hidden Treasures' );
 * // returns 'Hidden Treasures'
 */
-declare function capitalize( str: string ): string;
+declare function capitalize<S extends string>( str: S ): Capitalize<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/capitalize/docs/types/test.ts b/lib/node_modules/@stdlib/string/capitalize/docs/types/test.ts
index 508d191b4e10..621a6c85cb94 100644
--- a/lib/node_modules/@stdlib/string/capitalize/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/capitalize/docs/types/test.ts
@@ -21,9 +21,13 @@ import capitalize = require( './index' );
 
 // TESTS //
 
-// The function returns a string...
+// The function returns a capitalized string...
 {
-	capitalize( 'abc' ); // $ExpectType string
+	capitalize( 'abc' ); // $ExpectType "Abc"
+	capitalize( 'beep boop' ); // $ExpectType "Beep boop"
+	capitalize( 'a' ); // $ExpectType "A"
+	capitalize( 'A' ); // $ExpectType "A"
+	capitalize( 'abc' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/lowercase/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/lowercase/docs/types/index.d.ts
index 56d30464277e..2d0b221e4a8c 100644
--- a/lib/node_modules/@stdlib/string/lowercase/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/lowercase/docs/types/index.d.ts
@@ -28,7 +28,7 @@
 * var str = lowercase( 'bEEp' );
 * // returns 'beep'
 */
-declare function lowercase( str: string ): string;
+declare function lowercase<S extends string>( str: S ): Lowercase<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/lowercase/docs/types/test.ts b/lib/node_modules/@stdlib/string/lowercase/docs/types/test.ts
index 5e3fcaef9a91..0f9c14554d4f 100644
--- a/lib/node_modules/@stdlib/string/lowercase/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/lowercase/docs/types/test.ts
@@ -23,7 +23,9 @@ import lowercase = require( './index' );
 
 // The function returns a string...
 {
-	lowercase( 'abc' ); // $ExpectType string
+	lowercase( 'ABC' ); // $ExpectType "abc"
+	lowercase( 'Beep BOOP' ); // $ExpectType "beep boop"
+	lowercase( 'abc' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/uncapitalize/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/uncapitalize/docs/types/index.d.ts
index 0950b30c33d8..3b7c488f54e6 100644
--- a/lib/node_modules/@stdlib/string/uncapitalize/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/uncapitalize/docs/types/index.d.ts
@@ -18,6 +18,8 @@
 
 // TypeScript Version: 4.1
 
+type Uncapitalize<S extends string> = S extends `${infer F}${infer R}` ? `${Lowercase<F>}${R}` : S;
+
 /**
 * Uncapitalizes the first character of a string.
 *
@@ -40,7 +42,7 @@
 * var out = uncapitalize( 'Hidden Treasures' );
 * // returns 'hidden Treasures'
 */
-declare function uncapitalize( str: string ): string;
+declare function uncapitalize<S extends string>( str: S ): Uncapitalize<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/uncapitalize/docs/types/test.ts b/lib/node_modules/@stdlib/string/uncapitalize/docs/types/test.ts
index 82ca1b0f1ac9..b35d326b4d8b 100644
--- a/lib/node_modules/@stdlib/string/uncapitalize/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/uncapitalize/docs/types/test.ts
@@ -23,7 +23,11 @@ import uncapitalize = require( './index' );
 
 // The function returns a string...
 {
-	uncapitalize( 'Last man standing' ); // $ExpectType string
+	uncapitalize( 'Last man standing' ); // $ExpectType "last man standing"
+	uncapitalize( 'Hello World!' ); // $ExpectType "hello World!"
+	uncapitalize( 'BeepBoop' ); // $ExpectType "beepBoop"
+	uncapitalize( 'A' ); // $ExpectType "a"
+	uncapitalize( 'foo' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...
diff --git a/lib/node_modules/@stdlib/string/uppercase/docs/types/index.d.ts b/lib/node_modules/@stdlib/string/uppercase/docs/types/index.d.ts
index c8ea504b14b5..6254b6535f72 100644
--- a/lib/node_modules/@stdlib/string/uppercase/docs/types/index.d.ts
+++ b/lib/node_modules/@stdlib/string/uppercase/docs/types/index.d.ts
@@ -28,7 +28,7 @@
 * var str = uppercase( 'bEEp' );
 * // returns 'BEEP'
 */
-declare function uppercase( str: string ): string;
+declare function uppercase<S extends string>( str: S ): Uppercase<S>;
 
 
 // EXPORTS //
diff --git a/lib/node_modules/@stdlib/string/uppercase/docs/types/test.ts b/lib/node_modules/@stdlib/string/uppercase/docs/types/test.ts
index f9d11f96dbd5..2cadcfa6c2b4 100644
--- a/lib/node_modules/@stdlib/string/uppercase/docs/types/test.ts
+++ b/lib/node_modules/@stdlib/string/uppercase/docs/types/test.ts
@@ -23,7 +23,11 @@ import uppercase = require( './index' );
 
 // The function returns a string...
 {
-	uppercase( 'Last man standing' ); // $ExpectType string
+	uppercase( 'Last man standing' ); // $ExpectType "LAST MAN STANDING"
+	uppercase( 'Hello World!' ); // $ExpectType "HELLO WORLD!"
+	uppercase( 'beep' ); // $ExpectType "BEEP"
+	uppercase( 'BOOP' ); // $ExpectType "BOOP"
+	uppercase( 'foo' as string ); // $ExpectType string
 }
 
 // The compiler throws an error if the function is provided a value other than a string...