diff --git a/internal/sass/_string-ext.scss b/internal/sass/_string-ext.scss
deleted file mode 100644
index 0f891446b4..0000000000
--- a/internal/sass/_string-ext.scss
+++ /dev/null
@@ -1,195 +0,0 @@
-//
-// Copyright 2021 Google LLC
-// SPDX-License-Identifier: Apache-2.0
-//
-
-// go/keep-sorted start
-@use 'sass:list';
-@use 'sass:string';
-// go/keep-sorted end
-
-/// Checks if a string starts with a given prefix.
-///
-/// @example - scss
-///   @debug has-prefix('var(--foo)', 'var('); // true
-///
-/// @param {String} $string - The string to test.
-/// @param {String} $prefix - The prefix to check.
-/// @return {Boolean} True if the string starts with the given prefix.
-@function has-prefix($string, $prefix) {
-  @return string.slice($string, 1, string.length($prefix)) == $prefix;
-}
-
-/// Checks if a string ends with a given suffix.
-///
-/// @example - scss
-///   @debug has-suffix('var(--foo)', ')'); // true
-///
-/// @param {String} $string - The string to test.
-/// @param {String} $suffix - The suffix to check.
-/// @return {Boolean} True if the string ends with the given suffix.
-@function has-suffix($string, $suffix) {
-  @return string.slice($string, -1 * string.length($suffix)) == $suffix;
-}
-
-/// Trims a repeating prefix from the start of a string.
-///
-/// @example - scss
-///   @debug trim-repeating-prefix('  foo bar  ', ' '); // "foo bar  "
-///
-/// @param {String} $string - The string to trim.
-/// @param {String} $prefix - The repeating prefix string to trim.
-/// @return {String} The string with the prefix trimmed from the start.
-@function trim-repeating-prefix($string, $prefix) {
-  @while has-prefix($string, $prefix) {
-    $string: trim-prefix($string, $prefix);
-  }
-
-  @return $string;
-}
-
-/// Trims a prefix from the start of a string.
-///
-/// @example - scss
-///   @debug trim-prefix('var(--foo)', 'var('); // "--foo)"
-///
-/// @param {String} $string - The string to trim.
-/// @param {String} $prefix - The prefix string to trim.
-/// @return {String} The string with the prefix trimmed from the start.
-@function trim-prefix($string, $prefix) {
-  @if has-prefix($string, $prefix) {
-    $string: string.slice($string, string.length($prefix) + 1);
-  }
-
-  @return $string;
-}
-
-/// Trims a repeating suffix from the end of a string.
-///
-/// @example - scss
-///   @debug trim-repeating-suffix('  foo bar  ', ' '); // "  foo bar"
-///   @debug trim-repeating-suffix('var(--foo)', ')'); // "var(--foo"
-///
-/// @param {String} $string - The string to trim.
-/// @param {String} $suffix - The repeating suffix string to trim.
-/// @return {String} The string with the suffix trimmed from the end.
-@function trim-repeating-suffix($string, $suffix) {
-  @while has-suffix($string, $suffix) {
-    $string: trim-suffix($string, $suffix);
-  }
-
-  @return $string;
-}
-
-/// Trims a suffix from the end of a string.
-///
-/// @example - scss
-///   @debug trim-suffix('var(--foo)', ')'); // "var(--foo"
-///
-/// @param {String} $string - The string to trim.
-/// @param {String} $suffix - The suffix string to trim.
-/// @return {String} The string with the suffix trimmed from the end.
-@function trim-suffix($string, $suffix) {
-  @if has-suffix($string, $suffix) {
-    $string: string.slice($string, 1, -1 * string.length($suffix) - 1);
-  }
-
-  @return $string;
-}
-
-/// Trims a repeating prefix and suffix from the start and end of a string.
-///
-/// If a suffix is not provided, the prefix is used as the suffix to trim.
-///
-/// @example - scss
-///   @debug trim-repeating('  foo bar  ', ' '); // "foo bar"
-///
-/// @param {String} $string - The string to trim.
-/// @param {String} $prefix - The repeating prefix string to trim.
-/// @param {String} $suffix [$prefix] - The repeating suffix string to trim.
-/// @return {String} The string with the prefix and suffix trimmed.
-@function trim-repeating($string, $prefix, $suffix: $prefix) {
-  @return trim-repeating-prefix(
-    trim-repeating-suffix($string, $suffix),
-    $prefix
-  );
-}
-
-/// Trims a prefix and suffix from the start and end of a string.
-///
-/// If a suffix is not provided, the prefix is used as the suffix to trim.
-///
-/// @example - scss
-///   @debug trim('var(--foo)', 'var(', ')'); // "--foo"
-///
-/// @param {String} $string - The string to trim.
-/// @param {String} $prefix - The prefix string to trim.
-/// @param {String} $suffix [$prefix] - The suffix string to trim.
-/// @return {String} The string with the prefix and suffix trimmed.
-@function trim($string, $prefix, $suffix: $prefix) {
-  @return trim-prefix(trim-suffix($string, $suffix), $prefix);
-}
-
-/// Returns a new string with the first match of a pattern replaced by a
-/// replacement.
-///
-/// @example - scss
-///   @debug trim('foo bar baz', 'bar', 'quux'); // "foo quux baz"
-///
-/// @param {String} $string - The string to be searched.
-/// @param {String} $pattern - The pattern to search for.
-/// @param {String} $replacement - The value to replace the pattern.
-/// @return {String} The string with the first match of pattern replaced by the
-///     replacement or the initial string itself.
-@function replace($string, $pattern, $replacement) {
-  $pattern-index: string.index($string, $pattern);
-  @if not $pattern-index {
-    @return $string;
-  }
-
-  $before: string.slice($string, 1, $pattern-index - 1);
-  $after: string.slice($string, string.length($pattern) + $pattern-index);
-
-  @return $before + $replacement + $after;
-}
-
-/// Divides a string into an ordered list of substrings.
-///
-/// @example - scss
-///   @debug split("1px 2px 3px 4px"); // (1px 2px 3px 4px)
-///   @debug split("1px, 2px, 3px, 4px"); // (1px 2px 3px 4px)
-///   @debug split("1px/2px/3px/4px"); // (1px 2px 3px 4px)
-///
-/// @param {String} $str - The string to split
-/// @return {List} The list of substrings
-@function split($str) {
-  $list: ();
-  $item: '';
-  // list separator precedence is comma, slash, space
-  $separator: ' ';
-  @if string.index($str, ',') {
-    $separator: ',';
-  } @else if string.index($str, '/') {
-    $separator: '/';
-  }
-  @for $i from 1 through string.length($str) {
-    $chr: string.slice($str, $i, $i);
-    @if $chr == $separator {
-      @if $item != '' {
-        // remove surrounding whitespace
-        $item: string.unquote(trim($item, ' '));
-        $list: list.append($list, $item);
-      }
-      $item: '';
-    } @else {
-      $item: $item + $chr;
-    }
-  }
-  // append final item
-  @if $item != '' {
-    // remove surrounding whitespace
-    $item: string.unquote(trim($item, ' '));
-    $list: list.append($list, $item);
-  }
-  @return $list;
-}
diff --git a/internal/sass/_var.scss b/internal/sass/_var.scss
index 6787cfffdd..ce5ac36b7d 100644
--- a/internal/sass/_var.scss
+++ b/internal/sass/_var.scss
@@ -9,7 +9,7 @@
 @use 'sass:string';
 // go/keep-sorted end
 // go/keep-sorted start
-@use './string-ext';
+@use '../../sass/ext/string_ext';
 // go/keep-sorted end
 
 /// Creates a custom property `var()` string.
@@ -51,7 +51,7 @@
 /// @param {String} $name - The name of the custom property.
 /// @return {String} The full valid CSS custom property variable name.
 @function create-name($name) {
-  @if string-ext.has-prefix($name, '--') {
+  @if string_ext.starts-with($name, '--') {
     @return $name;
   }
 
@@ -173,7 +173,8 @@
 /// @return {Bool} True if the value is a custom property `var()` string, or
 ///     false if not.
 @function _is-var-string($var) {
-  @return meta.type-of($var) == 'string' and string-ext.has-prefix($var, 'var(');
+  @return meta.type-of($var) == 'string' and
+    string_ext.starts-with($var, 'var(');
 }
 
 /// Parses a `var()` string into a Map with `name` and `fallback` keys. This
@@ -197,14 +198,15 @@
   }
 
   // Remove function name and parens
-  $var: string-ext.trim($var, 'var(', ')');
+  $var: string_ext.replace-start($var, 'var(', '');
+  $var: string_ext.replace-end($var, ')', '');
 
-  $name: string-ext.trim-repeating($var, ' ');
+  $name: string_ext.trim($var);
   $fallback: null;
   $comma: string.index($var, ',');
   @if $comma != null {
-    $name: string-ext.trim-repeating(string.slice($var, 1, $comma - 1), ' ');
-    $fallback: string-ext.trim-repeating(string.slice($var, $comma + 1), ' ');
+    $name: string_ext.trim(string.slice($var, 1, $comma - 1));
+    $fallback: string_ext.trim(string.slice($var, $comma + 1));
     @if _is-var-string($fallback) {
       $fallback: _parse($fallback);
       @if $fallback == null {
diff --git a/internal/sass/test/_string-ext.test.scss b/internal/sass/test/_string-ext.test.scss
deleted file mode 100644
index 9c4947bfa6..0000000000
--- a/internal/sass/test/_string-ext.test.scss
+++ /dev/null
@@ -1,200 +0,0 @@
-//
-// Copyright 2021 Google LLC
-// SPDX-License-Identifier: Apache-2.0
-//
-
-// go/keep-sorted start
-@use 'sass:list';
-@use 'sass:meta';
-@use 'true' as test;
-// go/keep-sorted end
-// go/keep-sorted start
-@use '../string-ext';
-// go/keep-sorted end
-
-@include test.describe('string-ext') {
-  @include test.describe('has-prefix()') {
-    @include test.it('should return true if the string has the prefix') {
-      @include test.assert-true(string-ext.has-prefix('foo', 'f'));
-    }
-
-    @include test.it(
-      'should return false if the string does not have the prefix'
-    ) {
-      @include test.assert-false(string-ext.has-prefix('foo', 'b'));
-    }
-  }
-
-  @include test.describe('has-suffix()') {
-    @include test.it('should return true if the string has the suffix') {
-      @include test.assert-true(string-ext.has-suffix('foo', 'o'));
-    }
-
-    @include test.it(
-      'should return false if the string does not have the suffix'
-    ) {
-      @include test.assert-false(string-ext.has-suffix('foo', 'b'));
-    }
-  }
-
-  @include test.describe('trim-repeating-prefix()') {
-    @include test.it('should return the string with the prefix removed') {
-      @include test.assert-equal(
-        string-ext.trim-repeating-prefix('foo', 'fo'),
-        'o'
-      );
-    }
-
-    @include test.it(
-      'should return the string with a repeating prefix removed'
-    ) {
-      @include test.assert-equal(
-        string-ext.trim-repeating-prefix('babar', 'ba'),
-        'r'
-      );
-    }
-
-    @include test.it('should do nothing if the prefix does not exist') {
-      @include test.assert-equal(
-        string-ext.trim-repeating-prefix('foo', 'bar'),
-        'foo'
-      );
-    }
-  }
-
-  @include test.describe('trim-prefix()') {
-    @include test.it('should only trim the prefix once') {
-      @include test.assert-equal(string-ext.trim-prefix('babar', 'ba'), 'bar');
-    }
-  }
-
-  @include test.describe('trim-repeating-suffix()') {
-    @include test.it('should return the string with the suffix removed') {
-      @include test.assert-equal(
-        string-ext.trim-repeating-suffix('babar', 'bar'),
-        'ba'
-      );
-    }
-
-    @include test.it(
-      'should return the string with a repeating suffix removed'
-    ) {
-      @include test.assert-equal(
-        string-ext.trim-repeating-suffix('foo', 'o'),
-        'f'
-      );
-    }
-
-    @include test.it('should do nothing if the suffix does not exist') {
-      @include test.assert-equal(
-        string-ext.trim-repeating-suffix('foo', 'bar'),
-        'foo'
-      );
-    }
-  }
-
-  @include test.describe('trim-suffix()') {
-    @include test.it('should only trim the suffix once') {
-      @include test.assert-equal(string-ext.trim-suffix('foo', 'o'), 'fo');
-    }
-  }
-
-  @include test.describe('trim-repeating()') {
-    @include test.it('should trim the same repeating prefix and suffix') {
-      @include test.assert-equal(
-        string-ext.trim-repeating('  foo bar  ', ' '),
-        'foo bar'
-      );
-    }
-
-    @include test.it('should trim different repeating prefixes and suffixes') {
-      @include test.assert-equal(
-        string-ext.trim-repeating('fffoo barrr', $prefix: 'f', $suffix: 'r'),
-        'oo ba'
-      );
-    }
-  }
-
-  @include test.describe('trim()') {
-    @include test.it('should trim the a single prefix and suffix') {
-      @include test.assert-equal(
-        string-ext.trim('  foo bar  ', ' '),
-        ' foo bar '
-      );
-    }
-
-    @include test.it('should trim different prefixes and suffixes') {
-      @include test.assert-equal(
-        string-ext.trim('fffoo barrr', $prefix: 'f', $suffix: 'r'),
-        'ffoo barr'
-      );
-    }
-  }
-
-  @include test.describe('replace()') {
-    @include test.it('should replace a pattern') {
-      @include test.assert-equal(
-        string-ext.replace('foo bar baz', 'foo', 'quux'),
-        'quux bar baz'
-      );
-
-      @include test.assert-equal(
-        string-ext.replace('foo bar baz', 'bar', 'quux'),
-        'foo quux baz'
-      );
-
-      @include test.assert-equal(
-        string-ext.replace('foo bar baz', 'baz', 'quux'),
-        'foo bar quux'
-      );
-    }
-
-    @include test.it('should return the string if pattern dont match') {
-      @include test.assert-equal(
-        string-ext.replace('foo bar baz', 'quux', 'womp'),
-        'foo bar baz'
-      );
-    }
-
-    @include test.it('replaces only first match') {
-      @include test.assert-equal(
-        string-ext.replace('womp womp', 'womp', 'doo'),
-        'doo womp'
-      );
-    }
-  }
-
-  @include test.describe('split()') {
-    @include test.it('should return a list') {
-      $result: string-ext.split('foo bar baz');
-      @include test.assert-equal(meta.type-of($result), 'list');
-    }
-
-    @include test.it('should return ordered substrings') {
-      $result: string-ext.split('foo bar baz');
-      $expected: (foo bar baz);
-      @include test.assert-equal(list.length($result), 3);
-      @include test.assert-equal($result, $expected);
-    }
-
-    @include test.it('should handle comma separated lists') {
-      $result: string-ext.split('foo, bar, baz');
-      $expected: (foo bar baz);
-      @include test.assert-equal(list.length($result), 3);
-      @include test.assert-equal($result, $expected);
-    }
-
-    @include test.it('should handle slash separated lists') {
-      $result: string-ext.split('foo/ bar/ baz');
-      $expected: (foo bar baz);
-      @include test.assert-equal(list.length($result), 3);
-      @include test.assert-equal($result, $expected);
-    }
-
-    @include test.it('should one-item list for simple strings') {
-      $result: string-ext.split('foo');
-      $expected: list.append((), foo);
-      @include test.assert-equal($result, $expected);
-    }
-  }
-}
diff --git a/sass/ext/_string_ext.scss b/sass/ext/_string_ext.scss
new file mode 100644
index 0000000000..89e9a265ec
--- /dev/null
+++ b/sass/ext/_string_ext.scss
@@ -0,0 +1,153 @@
+//
+// Copyright 2021 Google LLC
+// SPDX-License-Identifier: Apache-2.0
+//
+
+// Extensions to the go/sass:string built-in module.
+
+// go/keep-sorted start by_regex='(.+) prefix_order=sass:
+@use 'sass:list';
+@use 'sass:string';
+// go/keep-sorted end
+
+/// Checks if a string starts with a given prefix.
+///
+/// @example scss
+///   @debug string_ext.starts-with('var(--foo)', 'var('); // true
+///
+/// @param {string} $string - The string to test.
+/// @param {string} $prefix - The prefix to check.
+/// @return {boolean} True if the string starts with the given prefix.
+@function starts-with($string, $prefix) {
+  @return string.slice($string, 1, string.length($prefix)) == $prefix;
+}
+
+/// Checks if a string ends with a given suffix.
+///
+/// @example scss
+///   @debug string_ext.ends-with('var(--foo)', ')'); // true
+///
+/// @param {string} $string - The string to test.
+/// @param {string} $suffix - The suffix to check.
+/// @return {boolean} True if the string ends with the given suffix.
+@function ends-with($string, $suffix) {
+  @return string.slice($string, -1 * string.length($suffix)) == $suffix;
+}
+
+/// Trims leading whitespace from the start of a string.
+///
+/// @example scss
+///   @debug string_ext.trim-start('  foo bar  '); // "foo bar  "
+///
+/// @param {string} $string - The string to trim.
+/// @return {string} The string with whitespace trimmed from the start.
+@function trim-start($string) {
+  @while starts-with($string, ' ') {
+    $string: replace-start($string, ' ', '');
+  }
+
+  @return $string;
+}
+
+/// Trims trailing whitespace from the end of a string.
+///
+/// @example scss
+///   @debug string_ext.trim-end('  foo bar  '); // "  foo bar"
+///
+/// @param {string} $string - The string to trim.
+/// @return {string} The string with trailing whitespace trimmed from the end.
+@function trim-end($string) {
+  @while ends-with($string, ' ') {
+    $string: replace-end($string, ' ', '');
+  }
+
+  @return $string;
+}
+
+/// Trims leading and trailing whitespace from a string.
+///
+/// @example scss
+///   @debug string_ext.trim('  foo bar  '); // "foo bar"
+///
+/// @param {string} $string - The string to trim.
+/// @return {string} The string with leading and trailing whitespace trimmed.
+@function trim($string) {
+  @return trim-start(trim-end($string));
+}
+
+/// Returns a new string with the first match of a pattern replaced by a given
+/// string.
+///
+/// @example scss
+///   @debug string_ext.replace('foo bar baz', 'bar', 'quux'); // "foo quux baz"
+///
+/// @param {string} $string - The string to be searched.
+/// @param {string} $pattern - The pattern to search for.
+/// @param {string} $replacement - The value to replace the pattern.
+/// @return {string} The string with the first match of pattern replaced by the
+///     replacement or the initial string itself.
+@function replace($string, $pattern, $replacement) {
+  $pattern-index: string.index($string, $pattern);
+  @if not $pattern-index {
+    @return $string;
+  }
+
+  $before: string.slice($string, 1, $pattern-index - 1);
+  $after: string.slice($string, string.length($pattern) + $pattern-index);
+
+  @return $before + $replacement + $after;
+}
+
+/// Returns a new string with all matches of a pattern replaced by a given
+/// string.
+///
+/// @example scss
+///   @debug string_ext.replace-all('foo bar baz', 'ba', 'qua'); // "foo quar quaz"
+///
+/// @param {string} $string - The string to be searched.
+/// @param {string} $pattern - The pattern to search for.
+/// @param {string} $replacement - The value to replace the pattern.
+/// @return {string} The string with all matches of pattern replaced by the
+///     replacement or the initial string itself.
+@function replace-all($string, $pattern, $replacement) {
+  @while string.index($string, $pattern) {
+    $string: replace($string, $pattern, $replacement);
+  }
+
+  @return $string;
+}
+
+/// Returns a new string that replaces a prefix at the start of the string.
+///
+/// @example scss
+///   @debug string_ext.replace-start('var(--foo)', 'var(', ''); // "--foo)"
+///
+/// @param {string} $string - The string to be searched.
+/// @param {string} $prefix - The prefix string to replace.
+/// @param {string} $replacement - The value to replace the prefix.
+/// @return {string} The string with the prefix replaced.
+@function replace-start($string, $prefix, $replacement) {
+  @if starts-with($string, $prefix) {
+    $string: $replacement + string.slice($string, string.length($prefix) + 1);
+  }
+
+  @return $string;
+}
+
+/// Returns a new string that replaces a suffix at the end of the string.
+///
+/// @example scss
+///   @debug string_ext.replace-end('var(--foo)', ')', ''); // "var(--foo"
+///
+/// @param {string} $string - The string to be searched.
+/// @param {string} $suffix - The suffix string to replace.
+/// @param {string} $replacement - The value to replace the suffix.
+/// @return {string} The string with the suffix trimmed from the end.
+@function replace-end($string, $suffix, $replacement) {
+  @if ends-with($string, $suffix) {
+    $string: string.slice($string, 1, -1 * string.length($suffix) - 1) +
+      $replacement;
+  }
+
+  @return $string;
+}
diff --git a/sass/ext/_string_ext_test.scss b/sass/ext/_string_ext_test.scss
new file mode 100644
index 0000000000..6de00d60bb
--- /dev/null
+++ b/sass/ext/_string_ext_test.scss
@@ -0,0 +1,166 @@
+//
+// Copyright 2021 Google LLC
+// SPDX-License-Identifier: Apache-2.0
+//
+
+@use 'true' as test;
+
+// go/keep-sorted start by_regex='(.+) prefix_order=sass:
+@use 'sass:list';
+@use 'sass:meta';
+@use 'string_ext';
+// go/keep-sorted end
+
+@include test.describe('string_ext') {
+  @include test.describe('starts-with()') {
+    @include test.it('should return true if the string has the prefix') {
+      @include test.assert-true(string_ext.starts-with('foo', 'f'));
+    }
+
+    @include test.it(
+      'should return false if the string does not have the prefix'
+    ) {
+      @include test.assert-false(string_ext.starts-with('foo', 'b'));
+    }
+  }
+
+  @include test.describe('ends-with()') {
+    @include test.it('should return true if the string has the suffix') {
+      @include test.assert-true(string_ext.ends-with('foo', 'o'));
+    }
+
+    @include test.it(
+      'should return false if the string does not have the suffix'
+    ) {
+      @include test.assert-false(string_ext.ends-with('foo', 'b'));
+    }
+  }
+
+  @include test.describe('trim-start()') {
+    @include test.it(
+      'should return the string with leading whitespace removed'
+    ) {
+      @include test.assert-equal(string_ext.trim-start('  foo'), 'foo');
+    }
+
+    @include test.it('should do nothing if there is no leading whitespace') {
+      @include test.assert-equal(string_ext.trim-start('foo'), 'foo');
+    }
+  }
+
+  @include test.describe('trim-end()') {
+    @include test.it(
+      'should return the string with trailing whitespace removed'
+    ) {
+      @include test.assert-equal(string_ext.trim-end('bar  '), 'bar');
+    }
+
+    @include test.it('should do nothing if there is no trailing whitespace') {
+      @include test.assert-equal(string_ext.trim-end('bar'), 'bar');
+    }
+  }
+
+  @include test.describe('trim()') {
+    @include test.it('should trim leading and trailing whitespace') {
+      @include test.assert-equal(string_ext.trim('  foo bar  '), 'foo bar');
+    }
+  }
+
+  @include test.describe('replace()') {
+    @include test.it('should replace a pattern') {
+      @include test.assert-equal(
+        string_ext.replace('foo bar baz', 'foo', 'quux'),
+        'quux bar baz'
+      );
+
+      @include test.assert-equal(
+        string_ext.replace('foo bar baz', 'bar', 'quux'),
+        'foo quux baz'
+      );
+
+      @include test.assert-equal(
+        string_ext.replace('foo bar baz', 'baz', 'quux'),
+        'foo bar quux'
+      );
+    }
+
+    @include test.it('should return the string if pattern does not match') {
+      @include test.assert-equal(
+        string_ext.replace('foo bar baz', 'quux', 'womp'),
+        'foo bar baz'
+      );
+    }
+
+    @include test.it('replaces only first match') {
+      @include test.assert-equal(
+        string_ext.replace('womp womp', 'womp', 'doo'),
+        'doo womp'
+      );
+    }
+  }
+
+  @include test.describe('replace-all()') {
+    @include test.it('should replace a single pattern') {
+      @include test.assert-equal(
+        string_ext.replace-all('foo bar baz', 'foo', 'quux'),
+        'quux bar baz'
+      );
+
+      @include test.assert-equal(
+        string_ext.replace-all('foo bar baz', 'bar', 'quux'),
+        'foo quux baz'
+      );
+
+      @include test.assert-equal(
+        string_ext.replace-all('foo bar baz', 'baz', 'quux'),
+        'foo bar quux'
+      );
+    }
+
+    @include test.it('should return the string if pattern does not match') {
+      @include test.assert-equal(
+        string_ext.replace-all('foo bar baz', 'quux', 'womp'),
+        'foo bar baz'
+      );
+    }
+
+    @include test.it('replaces multiple matches') {
+      @include test.assert-equal(
+        string_ext.replace-all('womp womp', 'womp', 'doo'),
+        'doo doo'
+      );
+    }
+  }
+
+  @include test.describe('replace-start()') {
+    @include test.it('should replace the prefix of a string') {
+      @include test.assert-equal(
+        string_ext.replace-start('babar', 'ba', 'foo'),
+        'foobar'
+      );
+    }
+
+    @include test.it('should return the string if prefix does not match') {
+      @include test.assert-equal(
+        string_ext.replace-start('foo', 'bar', 'baz'),
+        'foo'
+      );
+    }
+  }
+
+  @include test.describe('replace-end()') {
+    @include test.it('should replace the suffix of a string') {
+      @include test.assert-equal(
+        string_ext.replace-end('foobar', 'bar', 'foo'),
+        'foofoo'
+      );
+    }
+
+    @include test.it('should return the string if suffix does not match') {
+      @include test.assert-equal(
+        string_ext.replace-end('foo', 'bar', 'baz'),
+        'foo'
+      );
+    }
+  }
+}
diff --git a/internal/sass/test/test.scss b/sass/ext/tests.scss
similarity index 61%
rename from internal/sass/test/test.scss
rename to sass/ext/tests.scss
index ce438ede06..ea754dccf1 100644
--- a/internal/sass/test/test.scss
+++ b/sass/ext/tests.scss
@@ -3,6 +3,10 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 
+@use 'true' as test with (
+  $catch-errors: true
+);
+
 // go/keep-sorted start
-@use './string-ext.test';
+@use 'string_ext_test';
 // go/keep-sorted end
diff --git a/tabs/internal/_tab.scss b/tabs/internal/_tab.scss
index 50493d823f..463c80871e 100644
--- a/tabs/internal/_tab.scss
+++ b/tabs/internal/_tab.scss
@@ -10,7 +10,6 @@
 // go/keep-sorted start
 @use '../../elevation/elevation';
 @use '../../focus/focus-ring';
-@use '../../internal/sass/string-ext';
 @use '../../ripple/ripple';
 @use '../../tokens';
 // go/keep-sorted end