diff --git a/composer.json b/composer.json
index cd01adc936..121047d516 100644
--- a/composer.json
+++ b/composer.json
@@ -97,6 +97,7 @@
     "replace": {
         "tempest/auth": "self.version",
         "tempest/cache": "self.version",
+        "tempest/class-variance": "self.version",
         "tempest/clock": "self.version",
         "tempest/command-bus": "self.version",
         "tempest/console": "self.version",
@@ -138,6 +139,7 @@
         "psr-4": {
             "Tempest\\Auth\\": "packages/auth/src",
             "Tempest\\Cache\\": "packages/cache/src",
+            "Tempest\\ClassVariance\\": "packages/class-variance/src",
             "Tempest\\Clock\\": "packages/clock/src",
             "Tempest\\CommandBus\\": "packages/command-bus/src",
             "Tempest\\Console\\": "packages/console/src",
@@ -171,6 +173,7 @@
             "Tempest\\Vite\\": "packages/vite/src"
         },
         "files": [
+            "packages/class-variance/src/functions.php",
             "packages/clock/src/functions.php",
             "packages/command-bus/src/functions.php",
             "packages/container/src/functions.php",
diff --git a/docs/3-packages/03-class-variance.md b/docs/3-packages/03-class-variance.md
new file mode 100644
index 0000000000..9b117db023
--- /dev/null
+++ b/docs/3-packages/03-class-variance.md
@@ -0,0 +1,343 @@
+---
+title: Class Variance
+description: "The Class Variance package can be used standalone or with Tempest framework to provide a tailwind-variants style CSS variant system."
+---
+## Introduction
+
+Class variance — a PHP package for building component CSS class strings with variants, compound variants, slot support, and conflict-aware merging. Heavily inspired by [CVA](https://cva.style) and [Tailwind-Variants](https://www.tailwind-variants.org/), but with the ability to extend and support other frameworks also.
+
+Two flavours:
+
+- **`cv()`** — separator-based merging, framework-agnostic CSS, somewhat limited by default but can be extended to support other frameworks.
+- **`tv()`** — builds on `cv()` with Tailwind-aware merging, aiming to provide the same outcomes as [tailwind-merge](https://github.com/dcastil/tailwind-merge).
+
+## Installation
+
+### With Tempest
+
+```bash
+composer require tempest/class-variance
+```
+
+Discovery handles the rest. The `CvMergerInitializer` and `TvMergerInitializer` are Discovered automatically, binding tagged `ClassMerger` singletons for injection.
+
+To customise the configuration, publish a config file:
+
+```bash
+./tempest class-variance:publish:config
+```
+
+This scaffolds a `class-variance.config.php` in your app's source directory that Tempest discovers automatically. You can, as with other packages, move this wherever you wish, as Discovery will handle that for you.
+
+### Standalone (without Tempest)
+
+```bash
+composer require tempest/class-variance
+```
+
+Import the helper functions and call them directly — no container required:
+
+```php
+use function Tempest\ClassVariance\cv;
+use function Tempest\ClassVariance\tv;
+```
+
+
+## `cv()` — Generic class variance
+
+`cv()` uses a separator heuristic to resolve conflicts: everything before the first `-` is treated as the group key, and the last class in a group wins.
+
+```php
+use function Tempest\ClassVariance\cv;
+
+$button = cv(
+    base: 'btn',
+    variants: [
+        'size' => [
+            'sm' => 'btn-sm',
+            'md' => 'btn-md',
+            'lg' => 'btn-lg',
+        ],
+        'color' => [
+            'primary' => 'btn-primary',
+            'danger'  => 'btn-danger',
+        ],
+    ],
+    defaultVariants: [
+        'size' => 'md',
+    ],
+);
+
+echo $button();                               // 'btn btn-md'
+echo $button(['color' => 'primary']);         // 'btn btn-md btn-primary'
+echo $button(['size' => 'lg', 'color' => 'danger']); // 'btn btn-lg btn-danger'
+```
+
+### Compound variants
+
+Apply extra classes only when multiple props match simultaneously:
+
+```php
+$badge = cv(
+    base: 'badge',
+    variants: [
+        'color'   => ['primary' => 'badge-primary', 'danger' => 'badge-danger'],
+        'outline' => ['true' => 'badge-outline'],
+    ],
+    compoundVariants: [
+        [
+            'color'   => 'danger',
+            'outline' => 'true',
+            'class'   => 'border-danger',
+        ],
+    ],
+    defaultVariants: ['color' => 'primary'],
+);
+
+echo $badge(['outline' => 'true']);                         // 'badge badge-primary badge-outline'
+echo $badge(['color' => 'danger', 'outline' => 'true']);   // 'badge badge-danger badge-outline border-danger'
+```
+
+### Slots
+
+Split the output across named slots — useful for multi-element components:
+
+```php
+$card = cv(
+    base: [
+        'base'   => 'card',
+        'header' => 'card-header',
+        'body'   => 'card-body',
+    ],
+    variants: [
+        'size' => [
+            'sm' => ['base' => 'card-sm', 'body' => 'p-2'],
+            'lg' => ['base' => 'card-lg', 'body' => 'p-8'],
+        ],
+    ],
+    defaultVariants: ['size' => 'sm'],
+);
+
+echo $card(slot: 'base');                    // 'card card-sm'
+echo $card(slot: 'header');                  // 'card-header'
+echo $card(['size' => 'lg'], slot: 'body');  // 'card-body p-8'
+```
+
+:::info
+When your base defines exactly one slot, the slot is inferred automatically, and will internally default to 'base' — you do not need to pass `slot:`.
+:::
+
+### Passing extra classes
+
+Pass `class` or `className` in the props to append caller-supplied classes (these go through the same merger):
+
+```php
+echo $button(['color' => 'primary', 'class' => 'w-full']); // 'btn btn-md btn-primary w-full'
+```
+
+:::info
+Generally speaking, standardise on using `class` - `className` is provided only as a syntax courtesy for users of other, older CVA tools which are using this, however consider best practice to use `class` going forward.
+:::
+
+
+## `tv()` — Tailwind-aware class variance
+
+`tv()` ships with the full Tailwind CSS class group definitions from `tailwind-merge`. Conflicting utilities are deduplicated automatically — `p-2 p-4` resolves to `p-4`, `bg-red-500 bg-blue-500` resolves to `bg-blue-500`. The package implements a 'right-wins' approach which ensures that custom classes always override the default.
+
+The API is identical to `cv()`:
+
+```php
+use function Tempest\ClassVariance\tv;
+
+$button = tv(
+    base: 'inline-flex items-center rounded px-3 py-1.5 text-sm font-medium',
+    variants: [
+        'intent' => [
+            'primary'   => 'bg-blue-600 text-white hover:bg-blue-700',
+            'secondary' => 'bg-gray-100 text-gray-900 hover:bg-gray-200',
+            'danger'    => 'bg-red-600 text-white hover:bg-red-700',
+        ],
+        'size' => [
+            'sm' => 'px-2 py-1 text-xs',
+            'lg' => 'px-4 py-2 text-base',
+        ],
+    ],
+    defaultVariants: ['intent' => 'primary'],
+);
+
+echo $button();                          // base + primary intent classes
+echo $button(['intent' => 'danger']);    // px-3 wins over default, bg-red-600 replaces bg-blue-600
+echo $button(['size' => 'sm']);          // px-2 py-1 text-xs override base padding and text size
+```
+
+The conflict resolution means a caller can safely pass overriding classes without knowing what the component already applies:
+
+```php
+// Caller overrides just the background — no class duplication
+echo $button(['intent' => 'primary', 'class' => 'bg-indigo-600']);
+// → '...text-white hover:bg-blue-700 bg-indigo-600'  (bg-blue-600 removed)
+```
+
+## Customising the Tailwind config
+
+### Publish the config file (Tempest)
+
+```bash
+./tempest class-variance:publish:config
+```
+
+The published file returns a `TailwindClassVarianceConfig` object that Tempest discovers automatically. We don't currently publish a GenericConfig file, but you can use the same stub to create your own.
+
+### Single callsite
+
+Pass `config:` directly to override for one specific call. Everything else in your app uses the default.
+
+```php
+$config = new TailwindClassVarianceConfig(prefix: 'tw-', extend: new Classmap(/* ... */));
+
+$button = tv(base: 'tw-rounded tw-px-3', config: $config);
+```
+
+### Whole component class
+
+Inject the tagged ClassMerger singleton. It picks up your app's config automatically.
+
+```php
+use Tempest\ClassVariance\ClassMerger;
+use Tempest\Container\Tag;
+
+final readonly class ButtonComponent
+{
+    public function __construct(
+        #[Tag('tv')] private ClassMerger $merger, // or Tag('cv')
+    ) {}
+
+    public function render(string $intent = 'primary'): string
+    {
+        $button = tv(
+            base: 'rounded px-3 py-1.5',
+            variants: ['intent' => ['primary' => 'bg-blue-600', 'danger' => 'bg-red-600']],
+        );
+
+        return $button(['intent' => $intent]);
+    }
+}
+
+final readonly class ButtonComponent
+{
+    public function __construct(
+        #[Tag('cv')] private ClassMerger $merger,
+    ) {}
+}
+```
+
+### Override the default for all usages
+
+Publish a config file and Tempest will discover it automatically. It is registered in the container and used by both the tagged ClassMerger singletons and any tv() / cv() function calls throughout your app — no config: argument needed anywhere.
+
+```php class-variance.config.php
+use Tempest\ClassVariance\Classmaps\Classmap;
+use Tempest\ClassVariance\Config\TailwindClassVarianceConfig;
+
+return new TailwindClassVarianceConfig(
+    prefix: 'tw-',
+    extend: new Classmap(
+        classGroups: [
+            'scrollbar' => [['scrollbar' => ['hide', 'default']]],
+        ],
+    ),
+);
+```
+
+```php class-variance.config.php
+use Tempest\ClassVariance\Config\GenericClassVarianceConfig;
+
+return new GenericClassVarianceConfig(separator: '__');
+```
+
+For standalone use (no Tempest container), pass `config:` at each callsite or assign it once via a shared variable in your bootstrap.
+
+## Implementing a custom CSS kit
+
+If you're using a CSS framework other than Tailwind you can provide your own conflict-resolution strategy by implementing `ClassVarianceConfig`.
+
+### 1. Implement `ClassMerger`
+
+```php
+use Tempest\ClassVariance\ClassMerger;
+
+final readonly class DaisyUiMerger implements ClassMerger
+{
+    public function merge(string ...$classes): string
+    {
+        // Last class per group wins. Group = everything before the first '-'.
+        $resolved = [];
+
+        foreach ($classes as $class) {
+            $group = str_contains($class, '-')
+                ? substr($class, 0, strpos($class, '-'))
+                : $class;
+
+            $resolved[$group] = $class;
+        }
+
+        return implode(' ', array_values($resolved));
+    }
+}
+```
+
+### 2. Implement `ClassVarianceConfig`
+
+```php
+use Tempest\ClassVariance\ClassMerger;
+use Tempest\ClassVariance\Config\ClassVarianceConfig;
+
+final class DaisyUiConfig implements ClassVarianceConfig
+{
+    public ClassMerger $merger {
+        get => new DaisyUiMerger();
+    }
+}
+```
+
+### 3. Pass your config to `cv()` or `tv()`
+
+```php
+$button = cv(
+    base: 'btn',
+    variants: [
+        'color' => ['primary' => 'btn-primary', 'ghost' => 'btn-ghost'],
+        'size'  => ['sm' => 'btn-sm', 'lg' => 'btn-lg'],
+    ],
+    config: new DaisyUiConfig(),
+);
+```
+
+### 4. Bind in Tempest (optional)
+
+Return your config object from a `*.config.php` file — Tempest will discover it automatically and use it for any `cv()` or `tv()` calls that don't receive an explicit `$config` argument:
+
+```php daisy-ui.config.php
+return new DaisyUiConfig();
+```
+
+Or bind it explicitly in an initializer if you need constructor arguments:
+
+```php
+use Tempest\Container\Container;
+use Tempest\Container\Initializer;
+use Tempest\Container\Singleton;
+
+final readonly class DaisyUiConfigInitializer implements Initializer
+{
+    #[Singleton]
+    public function initialize(Container $container): DaisyUiConfig
+    {
+        return new DaisyUiConfig();
+    }
+}
+```
+
+:::info
+If you do create a binding for a CSS UI kit, please consider [contributing](https://github.com/tempestphp/tempest-framework/pulls) it back!
+:::
\ No newline at end of file
diff --git a/packages/class-variance/.gitattributes b/packages/class-variance/.gitattributes
new file mode 100644
index 0000000000..3f7775660b
--- /dev/null
+++ b/packages/class-variance/.gitattributes
@@ -0,0 +1,14 @@
+# Exclude build/test files from the release
+.github/                  export-ignore
+tests/                    export-ignore
+.gitattributes            export-ignore
+.gitignore                export-ignore
+phpunit.xml               export-ignore
+README.md                 export-ignore
+
+# Configure diff output
+*.view.php diff=html
+*.php diff=php
+*.css diff=css
+*.html diff=html
+*.md diff=markdown
diff --git a/packages/class-variance/LICENSE.md b/packages/class-variance/LICENSE.md
new file mode 100644
index 0000000000..54215b7261
--- /dev/null
+++ b/packages/class-variance/LICENSE.md
@@ -0,0 +1,9 @@
+The MIT License (MIT)
+
+Copyright (c) 2024 Brent Roose brendt@stitcher.io
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/packages/class-variance/composer.json b/packages/class-variance/composer.json
new file mode 100644
index 0000000000..b839078e83
--- /dev/null
+++ b/packages/class-variance/composer.json
@@ -0,0 +1,24 @@
+{
+    "name": "tempest/class-variance",
+    "description": "The PHP framework that gets out of your way.",
+    "require": {
+        "php": "^8.5",
+        "tempest/core": "3.x-dev",
+        "tempest/support": "3.x-dev"
+    },
+    "autoload": {
+        "psr-4": {
+            "Tempest\\ClassVariance\\": "src"
+        },
+        "files": [
+            "src/functions.php"
+        ]
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Tempest\\ClassVariance\\Tests\\": "tests"
+        }
+    },
+    "license": "MIT",
+    "minimum-stability": "dev"
+}
diff --git a/packages/class-variance/phpunit.xml b/packages/class-variance/phpunit.xml
new file mode 100644
index 0000000000..94b26e80b6
--- /dev/null
+++ b/packages/class-variance/phpunit.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/11.4/phpunit.xsd"
+	bootstrap="vendor/autoload.php"
+	executionOrder="depends,defects"
+	beStrictAboutOutputDuringTests="true"
+	displayDetailsOnPhpunitDeprecations="true"
+	failOnPhpunitDeprecation="false"
+	failOnRisky="true"
+	failOnWarning="true"
+>
+	<testsuites>
+		<testsuite name="Tempest Class Variance">
+			<directory>tests</directory>
+		</testsuite>
+	</testsuites>
+	<source restrictNotices="true" restrictWarnings="true" ignoreIndirectDeprecations="true">
+		<include>
+			<directory>src</directory>
+		</include>
+	</source>
+</phpunit>
diff --git a/packages/class-variance/src/ClassMerger.php b/packages/class-variance/src/ClassMerger.php
new file mode 100644
index 0000000000..791096a4a6
--- /dev/null
+++ b/packages/class-variance/src/ClassMerger.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+/**
+ * Merges a flat list of CSS class strings, resolving conflicts
+ * so that later classes override earlier ones within the same group.
+ */
+interface ClassMerger
+{
+    /**
+     * Merge the given class strings, returning a single deduplicated string.
+     * Conflict resolution strategy is determined by the implementation.
+     */
+    public function merge(string ...$classes): string;
+}
diff --git a/packages/class-variance/src/ClassNames.php b/packages/class-variance/src/ClassNames.php
new file mode 100644
index 0000000000..7d51a2f4bd
--- /dev/null
+++ b/packages/class-variance/src/ClassNames.php
@@ -0,0 +1,110 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+/**
+ * Immutable value object representing a parsed, flat list of CSS class tokens.
+ *
+ * Handles all input shapes that appear in variant definitions:
+ *   - Plain string                → implicitly targets the 'base' slot only
+ *   - Indexed array of strings    → flat class list, implicitly 'base'
+ *   - Associative array           → slot-keyed map; extract by requested slot
+ *   - Bool                        → always empty (booleans are not class names)
+ *
+ * @internal
+ */
+final readonly class ClassNames
+{
+    /** @param list<string> $items */
+    private function __construct(
+        private array $items = [],
+    ) {}
+
+    /**
+     * Parse any variant value into a ClassNames instance for the given slot.
+     *
+     * A plain string or indexed array implicitly targets the 'base' slot.
+     * Passing $slot = '' is the passthrough context (e.g. extra $props['class'])
+     * and always emits the classes regardless of slot.
+     *
+     * @param string|list<string|array<string, mixed>|bool>|array<string, string|array<string, mixed>|bool>|bool $input
+     */
+    public static function of(string|array|bool $input, string $slot = ''): self
+    {
+        if (is_bool($input)) {
+            return new self();
+        }
+
+        if (is_string($input)) {
+            // Plain string implicitly targets 'base'. Skip for any other explicit slot.
+            if ($slot !== '' && $slot !== 'base') {
+                return new self();
+            }
+
+            return new self(self::tokenise($input));
+        }
+
+        // Indexed (list) array — implicitly 'base', same rule as plain string.
+        if (array_is_list($input)) {
+            if ($slot !== '' && $slot !== 'base') {
+                return new self();
+            }
+
+            $items = [];
+            foreach ($input as $entry) {
+                if (! is_string($entry)) {
+                    continue;
+                }
+
+                array_push($items, ...self::tokenise($entry));
+            }
+
+            return new self($items);
+        }
+
+        // Associative (slot-keyed) array — extract the requested slot's value.
+        $slotValue = $input[$slot] ?? null;
+
+        if ($slotValue === null || is_bool($slotValue)) {
+            return new self();
+        }
+
+        // Recurse with slot='' so the plain-string / list rules above apply
+        // without the 'base'-only guard (we have already resolved the slot key).
+        return self::of($slotValue, '');
+    }
+
+    public static function empty(): self
+    {
+        return new self();
+    }
+
+    public function concat(self $other): self
+    {
+        return new self([...$this->items, ...$other->items]);
+    }
+
+    /** @return list<string> */
+    public function toArray(): array
+    {
+        return array_values(array_unique(
+            array_filter($this->items, static fn (string $c) => $c !== ''),
+        ));
+    }
+
+    public function toString(): string
+    {
+        return implode(' ', $this->toArray());
+    }
+
+    /** @return list<string> */
+    private static function tokenise(string $value): array
+    {
+        return array_values(array_filter(
+            explode(' ', $value),
+            static fn (string $t) => $t !== '',
+        ));
+    }
+}
diff --git a/packages/class-variance/src/ClassVariance.php b/packages/class-variance/src/ClassVariance.php
new file mode 100644
index 0000000000..6c25f5e8e8
--- /dev/null
+++ b/packages/class-variance/src/ClassVariance.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+/**
+ * A callable that resolves CSS class strings from a variant definition.
+ * Implementations hold base classes, variants, compound variants, and defaults,
+ * and produce a merged class string for a given set of active props and slot.
+ */
+interface ClassVariance
+{
+    /**
+     * Resolve the class string for the given props and slot.
+     *
+     * @param array<string, string|bool|array<string, string|bool>> $props Active variant prop values.
+     * @param string $slot Named slot to resolve (e.g. 'base', 'label'). When omitted
+     *   and the base defines a single slot, that slot is inferred automatically.
+     */
+    public function __invoke(array $props = [], string $slot = ''): string;
+}
diff --git a/packages/class-variance/src/Classmaps/Classmap.php b/packages/class-variance/src/Classmaps/Classmap.php
new file mode 100644
index 0000000000..2eafa6e9ab
--- /dev/null
+++ b/packages/class-variance/src/Classmaps/Classmap.php
@@ -0,0 +1,132 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Classmaps;
+
+/**
+ * Immutable map of CSS class group definitions and their conflict rules.
+ *
+ * Each entry in $classGroups maps a group ID to a list of matchers.
+ * Three matcher shapes are supported:
+ *
+ *   string                         → exact class name match
+ *                                    e.g. 'block' matches only 'block'
+ *
+ *   ['prefix']                     → wildcard prefix match
+ *                                    e.g. ['p'] matches 'p', 'p-4', 'p-[2rem]'
+ *
+ *   ['prefix' => ['v1', 'v2']]    → constrained prefix match
+ *                                    matches 'prefix-v1', 'prefix-v2', etc.
+ *                                    Use '' as a suffix to match the bare prefix
+ *                                    e.g. ['border' => ['', '2', '4']] matches
+ *                                    'border', 'border-2', 'border-4'
+ *
+ * Iteration order determines priority: the first group whose matcher fires wins.
+ * Constrained prefix groups should come before wildcard prefix groups when both
+ * share the same prefix (e.g. font-size before text-color for the 'text' prefix).
+ *
+ * $conflictingClassGroups maps a group ID to the list of group IDs it supersedes.
+ * When a class from group A is encountered during merge, all previously accumulated
+ * classes from groups listed under A are removed.
+ *
+ * Use extend() to merge additional definitions on top of an existing map (additive),
+ * or override() to replace specific group definitions entirely.
+ */
+final readonly class Classmap
+{
+    /**
+     * @param array<string, list<string|array<string, list<string>>|array{0: string}>> $classGroups
+     * @param array<string, list<string>> $conflictingClassGroups
+     */
+    public function __construct(
+        public array $classGroups = [],
+        public array $conflictingClassGroups = [],
+    ) {}
+
+    /**
+     * Find the group ID for the given class, or null if unknown.
+     */
+    public function findGroup(string $class): ?string
+    {
+        foreach ($this->classGroups as $groupId => $matchers) {
+            foreach ($matchers as $matcher) {
+                if (is_string($matcher)) {
+                    // Exact match
+                    if ($matcher === $class) {
+                        return $groupId;
+                    }
+
+                    continue;
+                }
+
+                if (array_is_list($matcher)) {
+                    // ['prefix'] — wildcard: matches prefix itself or prefix-{anything}
+                    $prefix = $matcher[0];
+
+                    if ($class === $prefix || str_starts_with($class, $prefix . '-')) {
+                        return $groupId;
+                    }
+                } else {
+                    // ['prefix' => ['suffix1', 'suffix2']] — constrained suffix list
+                    $prefix = (string) array_key_first($matcher);
+                    /** @var list<string> $suffixes */
+                    $suffixes = $matcher[$prefix];
+
+                    foreach ($suffixes as $suffix) {
+                        if ($suffix === '' && $class === $prefix) {
+                            return $groupId;
+                        }
+
+                        if ($suffix !== '' && $class === $prefix . '-' . $suffix) {
+                            return $groupId;
+                        }
+                    }
+                }
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Return a new map with $additions merged in.
+     * For groups that exist in both maps, matchers are concatenated (additive).
+     * Conflicting group lists are merged by union.
+     */
+    public function extend(self $additions): self
+    {
+        $groups = $this->classGroups;
+
+        foreach ($additions->classGroups as $groupId => $matchers) {
+            /** @var list<string|array<string, list<string>>|array{0: string}> $merged */
+            $merged = array_merge($groups[$groupId] ?? [], $matchers);
+            $groups[$groupId] = $merged;
+        }
+
+        $conflicts = $this->conflictingClassGroups;
+
+        foreach ($additions->conflictingClassGroups as $groupId => $conflicting) {
+            $conflicts[$groupId] = array_values(array_unique([
+                ...($conflicts[$groupId] ?? []),
+                ...$conflicting,
+            ]));
+        }
+
+        return new self($groups, $conflicts);
+    }
+
+    /**
+     * Return a new map with specific groups replaced entirely by $replacements.
+     * Groups not present in $replacements are kept as-is.
+     */
+    public function override(self $replacements): self
+    {
+        /** @var array<string, list<string|array<string, list<string>>|array{0: string}>> $newGroups */
+        $newGroups = array_replace($this->classGroups, $replacements->classGroups);
+        /** @var array<string, list<string>> $newConflicts */
+        $newConflicts = array_replace($this->conflictingClassGroups, $replacements->conflictingClassGroups);
+
+        return new self($newGroups, $newConflicts);
+    }
+}
diff --git a/packages/class-variance/src/Classmaps/GenericClassmap.php b/packages/class-variance/src/Classmaps/GenericClassmap.php
new file mode 100644
index 0000000000..d3a2d82e87
--- /dev/null
+++ b/packages/class-variance/src/Classmaps/GenericClassmap.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Classmaps;
+
+/**
+ * An empty Classmap — the default starting point for cv().
+ *
+ * No groups are declared, so the SeparatorClassMerger falls back purely to
+ * its separator heuristic (everything before the first '-' is the group key).
+ *
+ * Pass a Classmap with explicit groups to GenericClassVarianceConfig when you
+ * need conflict resolution for classes that share no common prefix.
+ */
+final class GenericClassmap
+{
+    public static function default(): Classmap
+    {
+        return new Classmap();
+    }
+}
diff --git a/packages/class-variance/src/Classmaps/TailwindClassmap.php b/packages/class-variance/src/Classmaps/TailwindClassmap.php
new file mode 100644
index 0000000000..3840193641
--- /dev/null
+++ b/packages/class-variance/src/Classmaps/TailwindClassmap.php
@@ -0,0 +1,450 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Classmaps;
+
+/**
+ * Default Tailwind CSS v3/v4 class group definitions and conflict rules.
+ *
+ * Ported from tailwind-merge (MIT) and verified against:
+ * https://github.com/tales-from-a-dev/tailwind-merge-php/blob/main/src/Support/Config.php
+ *
+ * Matcher shapes (see Classmap for full documentation):
+ *   string                       → exact class name
+ *   ['prefix']                   → wildcard prefix (any suffix)
+ *   ['prefix' => ['v1', 'v2']]  → constrained prefix (named suffixes only)
+ *
+ * Groups sharing a prefix use constrained matchers for the scale/size group and
+ * wildcard matchers for the color group. Since iteration order determines priority,
+ * the scale group must appear before the color group in the returned array.
+ *
+ * Known limitation: arbitrary values (e.g. border-[3px]) are not disambiguated
+ * from color values — they fall through to the color group. Full disambiguation
+ * requires validator callbacks, which can be added via extend().
+ */
+final class TailwindClassmap
+{
+    public static function default(): Classmap
+    {
+        return new Classmap(
+            classGroups: self::classGroups(),
+            conflictingClassGroups: self::conflictingClassGroups(),
+        );
+    }
+
+    /** @return array<string, list<string|array<string, list<string>>|array{0: string}>> */
+    private static function classGroups(): array
+    {
+        // Common scale values reused across groups
+        $borderWidthScale = ['', '0', '2', '4', '8'];
+        $tshirtScale = ['xs', 'sm', 'base', 'md', 'lg', 'xl', '2xl', '3xl', '4xl', '5xl', '6xl', '7xl', '8xl', '9xl'];
+        $fontSizeScale = ['xs', 'sm', 'base', 'lg', 'xl', '2xl', '3xl', '4xl', '5xl', '6xl', '7xl', '8xl', '9xl'];
+        $shadowScale = ['', 'sm', 'md', 'lg', 'xl', '2xl', 'inner', 'none'];
+
+        return [
+            // ── Layout ───────────────────────────────────────────────────────────
+
+            'aspect' => [['aspect']],
+            'container' => ['container'],
+            'columns' => [['columns']],
+            'break-after' => [['break-after' => ['auto', 'avoid', 'all', 'avoid-page', 'page', 'left', 'right', 'column']]],
+            'break-before' => [['break-before' => ['auto', 'avoid', 'all', 'avoid-page', 'page', 'left', 'right', 'column']]],
+            'break-inside' => [['break-inside' => ['auto', 'avoid', 'avoid-page', 'avoid-column']]],
+            'box-decoration' => [['box-decoration' => ['clone', 'slice']]],
+            'box' => [['box' => ['border', 'content']]],
+            'display' => [
+                'block',
+                'inline-block',
+                'inline',
+                'flex',
+                'inline-flex',
+                'table',
+                'inline-table',
+                'table-caption',
+                'table-cell',
+                'table-column',
+                'table-column-group',
+                'table-footer-group',
+                'table-header-group',
+                'table-row-group',
+                'table-row',
+                'flow-root',
+                'grid',
+                'inline-grid',
+                'contents',
+                'list-item',
+                'hidden',
+            ],
+            'float' => [['float' => ['start', 'end', 'right', 'left', 'none']]],
+            'clear' => [['clear' => ['start', 'end', 'right', 'left', 'both', 'none']]],
+            'isolation' => ['isolate', 'isolation-auto'],
+            'object-fit' => [['object' => ['contain', 'cover', 'fill', 'none', 'scale-down']]],
+            'object-position' => [['object' => ['bottom', 'center', 'left', 'left-bottom', 'left-top', 'right', 'right-bottom', 'right-top', 'top']]],
+            'overflow' => [['overflow' => ['auto', 'hidden', 'clip', 'visible', 'scroll']]],
+            'overflow-x' => [['overflow-x' => ['auto', 'hidden', 'clip', 'visible', 'scroll']]],
+            'overflow-y' => [['overflow-y' => ['auto', 'hidden', 'clip', 'visible', 'scroll']]],
+            'overscroll' => [['overscroll' => ['auto', 'contain', 'none']]],
+            'overscroll-x' => [['overscroll-x' => ['auto', 'contain', 'none']]],
+            'overscroll-y' => [['overscroll-y' => ['auto', 'contain', 'none']]],
+            'position' => ['static', 'fixed', 'absolute', 'relative', 'sticky'],
+            'inset' => [['inset']],
+            'inset-x' => [['inset-x']],
+            'inset-y' => [['inset-y']],
+            'start' => [['start']],
+            'end' => [['end']],
+            'top' => [['top']],
+            'right' => [['right']],
+            'bottom' => [['bottom']],
+            'left' => [['left']],
+            'visibility' => ['visible', 'invisible', 'collapse'],
+            'z' => [['z']],
+
+            // ── Flexbox & Grid ────────────────────────────────────────────────────
+
+            'basis' => [['basis']],
+            'flex-direction' => [['flex' => ['row', 'row-reverse', 'col', 'col-reverse']]],
+            'flex-wrap' => [['flex' => ['wrap', 'wrap-reverse', 'nowrap']]],
+            'flex' => [['flex']],
+            'grow' => [['grow']],
+            'shrink' => [['shrink']],
+            'order' => [['order']],
+            'grid-cols' => [['grid-cols']],
+            'grid-rows' => [['grid-rows']],
+            'col-span' => [['col-span'], 'col-auto'],
+            'col-start' => [['col-start']],
+            'col-end' => [['col-end']],
+            'row-span' => [['row-span'], 'row-auto'],
+            'row-start' => [['row-start']],
+            'row-end' => [['row-end']],
+            'grid-flow' => [['grid-flow' => ['row', 'col', 'dense', 'row-dense', 'col-dense']]],
+            'auto-cols' => [['auto-cols']],
+            'auto-rows' => [['auto-rows']],
+            'gap' => [['gap']],
+            'gap-x' => [['gap-x']],
+            'gap-y' => [['gap-y']],
+            'justify-content' => [['justify' => ['normal', 'start', 'end', 'center', 'between', 'around', 'evenly', 'stretch']]],
+            'justify-items' => [['justify-items' => ['start', 'end', 'center', 'stretch']]],
+            'justify-self' => [['justify-self' => ['auto', 'start', 'end', 'center', 'stretch']]],
+            'align-content' => [['content' => ['normal', 'center', 'start', 'end', 'between', 'around', 'evenly', 'baseline', 'stretch']]],
+            'align-items' => [['items' => ['start', 'end', 'center', 'baseline', 'stretch']]],
+            'align-self' => [['self' => ['auto', 'start', 'end', 'center', 'stretch', 'baseline']]],
+            'place-content' => [['place-content' => ['center', 'start', 'end', 'between', 'around', 'evenly', 'baseline', 'stretch']]],
+            'place-items' => [['place-items' => ['start', 'end', 'center', 'baseline', 'stretch']]],
+            'place-self' => [['place-self' => ['auto', 'start', 'end', 'center', 'stretch']]],
+
+            // ── Spacing ───────────────────────────────────────────────────────────
+
+            'p' => [['p']],
+            'px' => [['px']],
+            'py' => [['py']],
+            'ps' => [['ps']],
+            'pe' => [['pe']],
+            'pt' => [['pt']],
+            'pr' => [['pr']],
+            'pb' => [['pb']],
+            'pl' => [['pl']],
+            'm' => [['m']],
+            'mx' => [['mx']],
+            'my' => [['my']],
+            'ms' => [['ms']],
+            'me' => [['me']],
+            'mt' => [['mt']],
+            'mr' => [['mr']],
+            'mb' => [['mb']],
+            'ml' => [['ml']],
+            'space-x' => [['space-x']],
+            'space-y' => [['space-y']],
+            'space-x-reverse' => ['space-x-reverse'],
+            'space-y-reverse' => ['space-y-reverse'],
+
+            // ── Sizing ────────────────────────────────────────────────────────────
+
+            'w' => [['w']],
+            'min-w' => [['min-w']],
+            'max-w' => [['max-w']],
+            'h' => [['h']],
+            'min-h' => [['min-h']],
+            'max-h' => [['max-h']],
+            'size' => [['size']],
+
+            // ── Typography ────────────────────────────────────────────────────────
+            // font-size uses constrained 'text' prefix; text-color uses wildcard.
+            // Iteration order ensures font-size is matched before text-color.
+
+            'font-size' => [['text' => $fontSizeScale]],
+            'font-smoothing' => ['antialiased', 'subpixel-antialiased'],
+            'font-style' => ['italic', 'not-italic'],
+            'font-weight' => [['font' => ['thin', 'extralight', 'light', 'normal', 'medium', 'semibold', 'bold', 'extrabold', 'black']]],
+            'font-family' => [['font']],
+            'font-variant-numeric' => [
+                'normal-nums',
+                'ordinal',
+                'slashed-zero',
+                'lining-nums',
+                'oldstyle-nums',
+                'proportional-nums',
+                'tabular-nums',
+                'diagonal-fractions',
+                'stacked-fractions',
+            ],
+            'tracking' => [['tracking' => ['tighter', 'tight', 'normal', 'wide', 'wider', 'widest']]],
+            'line-clamp' => [['line-clamp']],
+            'leading' => [['leading' => ['none', 'tight', 'snug', 'normal', 'relaxed', 'loose']]],
+            'list-image' => [['list-image']],
+            'list-style-position' => ['list-inside', 'list-outside'],
+            'list-style-type' => [['list' => ['none', 'disc', 'decimal']]],
+            'text-align' => [['text' => ['left', 'center', 'right', 'justify', 'start', 'end']]],
+            'text-color' => [['text']], // wildcard — catches anything not matched above
+            'text-decoration' => ['underline', 'overline', 'line-through', 'no-underline'],
+            'text-decoration-color' => [['decoration']],
+            'text-decoration-style' => [['decoration' => ['solid', 'double', 'dotted', 'dashed', 'wavy']]],
+            'text-decoration-thickness' => [['underline-offset']],
+            'text-transform' => ['uppercase', 'lowercase', 'capitalize', 'normal-case'],
+            'text-overflow' => ['truncate', 'text-ellipsis', 'text-clip'],
+            'text-wrap' => [['text' => ['wrap', 'nowrap', 'balance', 'pretty']]],
+            'indent' => [['indent']],
+            'vertical-align' => [['align' => ['baseline', 'top', 'middle', 'bottom', 'text-top', 'text-bottom', 'sub', 'super']]],
+            'whitespace' => [['whitespace' => ['normal', 'nowrap', 'pre', 'pre-line', 'pre-wrap', 'break-spaces']]],
+            'break-words' => [['break' => ['normal', 'words', 'all', 'keep']]],
+            'hyphens' => [['hyphens' => ['none', 'manual', 'auto']]],
+            'content' => [['content']],
+
+            // ── Backgrounds ───────────────────────────────────────────────────────
+
+            'bg-attach' => [['bg' => ['fixed', 'local', 'scroll']]],
+            'bg-clip' => [['bg-clip' => ['border', 'padding', 'content', 'text']]],
+            'bg-color' => [['bg']], // wildcard — catches bg-{color}
+            'bg-origin' => [['bg-origin' => ['border', 'padding', 'content']]],
+            'bg-position' => [['bg' => ['bottom', 'center', 'left', 'left-bottom', 'left-top', 'right', 'right-bottom', 'right-top', 'top']]],
+            'bg-repeat' => [['bg' => ['repeat', 'no-repeat', 'repeat-x', 'repeat-y', 'repeat-round', 'repeat-space']]],
+            'bg-size' => [['bg' => ['auto', 'cover', 'contain']]],
+            'bg-image' => [
+                ['bg' => ['none', 'gradient-to-t', 'gradient-to-tr', 'gradient-to-r', 'gradient-to-br', 'gradient-to-b', 'gradient-to-bl', 'gradient-to-l', 'gradient-to-tl']],
+            ],
+            'gradient-from' => [['from']],
+            'gradient-via' => [['via']],
+            'gradient-to' => [['to']],
+
+            // ── Borders ───────────────────────────────────────────────────────────
+            // border-w uses constrained suffix list; border-color uses wildcard.
+
+            'rounded' => [['rounded']],
+            'rounded-s' => [['rounded-s']],
+            'rounded-e' => [['rounded-e']],
+            'rounded-t' => [['rounded-t']],
+            'rounded-r' => [['rounded-r']],
+            'rounded-b' => [['rounded-b']],
+            'rounded-l' => [['rounded-l']],
+            'rounded-ss' => [['rounded-ss']],
+            'rounded-se' => [['rounded-se']],
+            'rounded-ee' => [['rounded-ee']],
+            'rounded-es' => [['rounded-es']],
+            'rounded-tl' => [['rounded-tl']],
+            'rounded-tr' => [['rounded-tr']],
+            'rounded-br' => [['rounded-br']],
+            'rounded-bl' => [['rounded-bl']],
+            'border-w' => [['border' => $borderWidthScale]], // constrained: border, border-0, border-2, border-4, border-8
+            'border-color' => [['border']], // wildcard: border-{color/anything-else}
+            'border-w-x' => [['border-x' => $borderWidthScale]],
+            'border-color-x' => [['border-x']],
+            'border-w-y' => [['border-y' => $borderWidthScale]],
+            'border-color-y' => [['border-y']],
+            'border-w-s' => [['border-s' => $borderWidthScale]],
+            'border-color-s' => [['border-s']],
+            'border-w-e' => [['border-e' => $borderWidthScale]],
+            'border-color-e' => [['border-e']],
+            'border-w-t' => [['border-t' => $borderWidthScale]],
+            'border-color-t' => [['border-t']],
+            'border-w-r' => [['border-r' => $borderWidthScale]],
+            'border-color-r' => [['border-r']],
+            'border-w-b' => [['border-b' => $borderWidthScale]],
+            'border-color-b' => [['border-b']],
+            'border-w-l' => [['border-l' => $borderWidthScale]],
+            'border-color-l' => [['border-l']],
+            'border-style' => [['border' => ['solid', 'dashed', 'dotted', 'double', 'hidden', 'none']]],
+            'divide-x' => [['divide-x' => $borderWidthScale]],
+            'divide-color-x' => [['divide-x']],
+            'divide-y' => [['divide-y' => $borderWidthScale]],
+            'divide-color-y' => [['divide-y']],
+            'divide-color' => [['divide']],
+            'divide-style' => [['divide' => ['solid', 'dashed', 'dotted', 'double', 'none']]],
+            'outline-w' => [['outline' => $borderWidthScale]],
+            'outline-color' => [['outline']],
+            'outline-style' => [['outline' => ['none', 'solid', 'dashed', 'dotted', 'double']]],
+            'outline-offset' => [['outline-offset']],
+            'ring-w' => [['ring' => ['', '0', '1', '2', '4', '8']]], // constrained: ring, ring-0, ring-1, ring-2, ring-4, ring-8
+            'ring-w-inset' => ['ring-inset'],
+            'ring-color' => [['ring']], // wildcard: ring-{color}
+            'ring-offset-w' => [['ring-offset' => $borderWidthScale]],
+            'ring-offset-color' => [['ring-offset']],
+
+            // ── Effects ───────────────────────────────────────────────────────────
+            // shadow uses constrained suffix list; shadow-color uses wildcard.
+
+            'shadow' => [['shadow' => $shadowScale]], // shadow, shadow-sm, shadow-md, shadow-lg, shadow-xl, shadow-2xl, shadow-inner, shadow-none
+            'shadow-color' => [['shadow']], // wildcard: shadow-{color}
+            'inset-shadow' => [['inset-shadow' => $shadowScale]],
+            'inset-shadow-color' => [['inset-shadow']],
+            'opacity' => [['opacity']],
+            'mix-blend' => [['mix-blend']],
+            'bg-blend' => [['bg-blend']],
+
+            // ── Filters ───────────────────────────────────────────────────────────
+
+            'filter' => ['filter', 'filter-none'],
+            'blur' => [['blur' => $tshirtScale]],
+            'brightness' => [['brightness']],
+            'contrast' => [['contrast']],
+            'drop-shadow' => [['drop-shadow' => $shadowScale]],
+            'drop-shadow-color' => [['drop-shadow']],
+            'grayscale' => [['grayscale' => ['', '0']]],
+            'hue-rotate' => [['hue-rotate']],
+            'invert' => [['invert' => ['', '0']]],
+            'saturate' => [['saturate']],
+            'sepia' => [['sepia' => ['', '0']]],
+            'backdrop-filter' => ['backdrop-filter', 'backdrop-filter-none'],
+            'backdrop-blur' => [['backdrop-blur' => $tshirtScale]],
+            'backdrop-brightness' => [['backdrop-brightness']],
+            'backdrop-contrast' => [['backdrop-contrast']],
+            'backdrop-grayscale' => [['backdrop-grayscale' => ['', '0']]],
+            'backdrop-hue-rotate' => [['backdrop-hue-rotate']],
+            'backdrop-invert' => [['backdrop-invert' => ['', '0']]],
+            'backdrop-opacity' => [['backdrop-opacity']],
+            'backdrop-saturate' => [['backdrop-saturate']],
+            'backdrop-sepia' => [['backdrop-sepia' => ['', '0']]],
+
+            // ── Transforms ────────────────────────────────────────────────────────
+
+            'transform' => [['transform' => ['', 'cpu', 'gpu', 'none']]],
+            'scale' => [['scale']],
+            'scale-x' => [['scale-x']],
+            'scale-y' => [['scale-y']],
+            'rotate' => [['rotate']],
+            'translate-x' => [['translate-x']],
+            'translate-y' => [['translate-y']],
+            'skew-x' => [['skew-x']],
+            'skew-y' => [['skew-y']],
+            'transform-origin' => [['origin']],
+            'perspective' => [['perspective' => ['dramatic', 'near', 'normal', 'midrange', 'distant', 'none']]],
+            'perspective-origin' => [['perspective-origin']],
+            'backface' => [['backface' => ['hidden', 'visible']]],
+
+            // ── Transitions & Animation ───────────────────────────────────────────
+
+            'transition' => [['transition']],
+            'duration' => [['duration']],
+            'ease' => [['ease' => ['linear', 'in', 'out', 'in-out']]],
+            'delay' => [['delay']],
+            'animate' => [['animate' => ['none', 'spin', 'ping', 'pulse', 'bounce']]],
+            'will-change' => [['will-change']],
+
+            // ── Interactivity ─────────────────────────────────────────────────────
+
+            'appearance' => [['appearance' => ['none', 'auto']]],
+            'cursor' => [['cursor']],
+            'caret-color' => [['caret']],
+            'pointer-events' => [['pointer-events' => ['none', 'auto']]],
+            'resize' => ['resize-none', 'resize-y', 'resize-x', 'resize'],
+            'scroll-behavior' => [['scroll' => ['auto', 'smooth']]],
+            'scroll-m' => [['scroll-m']],
+            'scroll-mx' => [['scroll-mx']],
+            'scroll-my' => [['scroll-my']],
+            'scroll-ms' => [['scroll-ms']],
+            'scroll-me' => [['scroll-me']],
+            'scroll-mt' => [['scroll-mt']],
+            'scroll-mr' => [['scroll-mr']],
+            'scroll-mb' => [['scroll-mb']],
+            'scroll-ml' => [['scroll-ml']],
+            'scroll-p' => [['scroll-p']],
+            'scroll-px' => [['scroll-px']],
+            'scroll-py' => [['scroll-py']],
+            'scroll-ps' => [['scroll-ps']],
+            'scroll-pe' => [['scroll-pe']],
+            'scroll-pt' => [['scroll-pt']],
+            'scroll-pr' => [['scroll-pr']],
+            'scroll-pb' => [['scroll-pb']],
+            'scroll-pl' => [['scroll-pl']],
+            'snap-align' => [['snap' => ['start', 'end', 'center', 'align-none']]],
+            'snap-stop' => [['snap' => ['normal', 'always']]],
+            'snap-type' => [['snap' => ['none', 'x', 'y', 'both']]],
+            'snap-strictness' => [['snap' => ['mandatory', 'proximity']]],
+            'touch' => [['touch']],
+            'select' => [['select' => ['none', 'text', 'all', 'auto']]],
+
+            // ── SVG ───────────────────────────────────────────────────────────────
+
+            'fill' => [['fill']],
+            'stroke-w' => [['stroke' => ['', '0', '1', '2']]],
+            'stroke-color' => [['stroke']],
+
+            // ── Accessibility ─────────────────────────────────────────────────────
+
+            'sr' => ['sr-only', 'not-sr-only'],
+
+            // ── Table ─────────────────────────────────────────────────────────────
+
+            'border-collapse' => [['border' => ['collapse', 'separate']]],
+            'border-spacing' => [['border-spacing']],
+            'border-spacing-x' => [['border-spacing-x']],
+            'border-spacing-y' => [['border-spacing-y']],
+            'caption-side' => [['caption' => ['top', 'bottom']]],
+            'table-layout' => [['table' => ['auto', 'fixed']]],
+        ];
+    }
+
+    /** @return array<string, list<string>> */
+    private static function conflictingClassGroups(): array
+    {
+        return [
+            'p' => ['px', 'py', 'ps', 'pe', 'pt', 'pr', 'pb', 'pl'],
+            'px' => ['ps', 'pe'],
+            'py' => ['pt', 'pb'],
+            'm' => ['mx', 'my', 'ms', 'me', 'mt', 'mr', 'mb', 'ml'],
+            'mx' => ['ms', 'me'],
+            'my' => ['mt', 'mb'],
+            'inset' => ['inset-x', 'inset-y', 'start', 'end', 'top', 'right', 'bottom', 'left'],
+            'inset-x' => ['start', 'end'],
+            'inset-y' => ['top', 'bottom'],
+            'gap' => ['gap-x', 'gap-y'],
+            'overflow' => ['overflow-x', 'overflow-y'],
+            'overscroll' => ['overscroll-x', 'overscroll-y'],
+            'rounded' => [
+                'rounded-s',
+                'rounded-e',
+                'rounded-t',
+                'rounded-r',
+                'rounded-b',
+                'rounded-l',
+                'rounded-ss',
+                'rounded-se',
+                'rounded-ee',
+                'rounded-es',
+                'rounded-tl',
+                'rounded-tr',
+                'rounded-br',
+                'rounded-bl',
+            ],
+            'rounded-t' => ['rounded-tl', 'rounded-tr'],
+            'rounded-r' => ['rounded-tr', 'rounded-br'],
+            'rounded-b' => ['rounded-br', 'rounded-bl'],
+            'rounded-l' => ['rounded-tl', 'rounded-bl'],
+            'rounded-s' => ['rounded-ss', 'rounded-es'],
+            'rounded-e' => ['rounded-se', 'rounded-ee'],
+            'border-w' => ['border-w-x', 'border-w-y', 'border-w-s', 'border-w-e', 'border-w-t', 'border-w-r', 'border-w-b', 'border-w-l'],
+            'border-w-x' => ['border-w-s', 'border-w-e'],
+            'border-w-y' => ['border-w-t', 'border-w-b'],
+            'border-color' => ['border-color-x', 'border-color-y', 'border-color-s', 'border-color-e', 'border-color-t', 'border-color-r', 'border-color-b', 'border-color-l'],
+            'border-color-x' => ['border-color-s', 'border-color-e'],
+            'border-color-y' => ['border-color-t', 'border-color-b'],
+            'scale' => ['scale-x', 'scale-y'],
+            'font-size' => ['leading'],
+            'scroll-m' => ['scroll-mx', 'scroll-my', 'scroll-ms', 'scroll-me', 'scroll-mt', 'scroll-mr', 'scroll-mb', 'scroll-ml'],
+            'scroll-mx' => ['scroll-ms', 'scroll-me'],
+            'scroll-my' => ['scroll-mt', 'scroll-mb'],
+            'scroll-p' => ['scroll-px', 'scroll-py', 'scroll-ps', 'scroll-pe', 'scroll-pt', 'scroll-pr', 'scroll-pb', 'scroll-pl'],
+            'scroll-px' => ['scroll-ps', 'scroll-pe'],
+            'scroll-py' => ['scroll-pt', 'scroll-pb'],
+        ];
+    }
+}
diff --git a/packages/class-variance/src/Commands/PublishConfigCommand.php b/packages/class-variance/src/Commands/PublishConfigCommand.php
new file mode 100644
index 0000000000..8604361653
--- /dev/null
+++ b/packages/class-variance/src/Commands/PublishConfigCommand.php
@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Commands;
+
+use Tempest\Console\ConsoleCommand;
+use Tempest\Console\HasConsole;
+use Tempest\Support\Filesystem;
+
+use function Tempest\root_path;
+use function Tempest\src_path;
+
+final class PublishConfigCommand
+{
+    use HasConsole;
+
+    #[ConsoleCommand(
+        name: 'class-variance:publish:config',
+        description: 'Publishes a class variance config file to your application',
+    )]
+    public function __invoke(): void
+    {
+        $suggested = src_path('class-variance.config.php');
+        $relative = ltrim(str_replace(root_path(), '', $suggested), '/\\');
+
+        $destination = $this->console->ask(
+            question: 'Where should the config file be created?',
+            default: $relative,
+        );
+
+        $destination = str_starts_with($destination, '/')
+            ? $destination
+            : root_path($destination);
+
+        if (Filesystem\is_file($destination)) {
+            $overwrite = $this->console->confirm(
+                question: "The file <em>{$relative}</em> already exists. Overwrite it?",
+                default: false,
+            );
+
+            if (! $overwrite) {
+                $this->console->info('Aborted.');
+
+                return;
+            }
+        }
+
+        Filesystem\ensure_directory_exists(dirname($destination));
+        Filesystem\write_file($destination, $this->stub());
+
+        $this->console->success("Config published to <em>{$relative}</em>.");
+    }
+
+    private function stub(): string
+    {
+        $stub = <<<'PHP'
+        <?php
+
+        declare(strict_types=1);
+
+        use Tempest\ClassVariance\Classmaps\Classmap;
+        use Tempest\ClassVariance\Config\TailwindClassVarianceConfig;
+
+        /**
+         * Class Variance configuration.
+         *
+         * This file is auto-discovered by Tempest. The object you return here is
+         * bound in the container and picked up by tv() and the TvMergerInitializer.
+         *
+         * Available options:
+         *
+         *   $prefix    — Tailwind class prefix, e.g. 'tw-' (default: '')
+         *   $separator — Variant separator, e.g. '_' (default: ':')
+         *   $extend    — Additive class-group definitions merged on top of the defaults
+         *   $override  — Class-group definitions that fully replace the matching defaults
+         *
+         * To add custom utilities you can use $extend:
+         *
+         *   $extend: new Classmap(
+         *       classGroups: [
+         *           'my-group' => ['my-class', ['my-prefix']],
+         *       ],
+         *       conflictingClassGroups: [
+         *           'my-group' => ['another-group'],
+         *       ],
+         *   ),
+         *
+         * For cv() / GenericClassVarianceConfig, swap TailwindClassVarianceConfig
+         * for GenericClassVarianceConfig and use its $separator and $classGroups options.
+         */
+        return new TailwindClassVarianceConfig(
+            prefix: '',
+            separator: ':',
+            extend: null,
+            override: null,
+        );
+        PHP;
+
+        return str_replace('        ', '', $stub);
+    }
+}
diff --git a/packages/class-variance/src/Config/ClassVarianceConfig.php b/packages/class-variance/src/Config/ClassVarianceConfig.php
new file mode 100644
index 0000000000..854f6eeb80
--- /dev/null
+++ b/packages/class-variance/src/Config/ClassVarianceConfig.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Config;
+
+use Tempest\ClassVariance\ClassMerger;
+
+/**
+ * Configuration object that supplies a ClassMerger to cv() and tv().
+ *
+ * Implement this interface to provide a completely custom merge strategy.
+ * For the built-in strategies use GenericClassVarianceConfig (cv)
+ * or TailwindClassVarianceConfig (tv).
+ */
+interface ClassVarianceConfig
+{
+    public ClassMerger $merger { get; }
+}
diff --git a/packages/class-variance/src/Config/GenericClassVarianceConfig.php b/packages/class-variance/src/Config/GenericClassVarianceConfig.php
new file mode 100644
index 0000000000..5fe91158a0
--- /dev/null
+++ b/packages/class-variance/src/Config/GenericClassVarianceConfig.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Config;
+
+use Tempest\ClassVariance\Classmaps\Classmap;
+use Tempest\ClassVariance\ClassMerger;
+use Tempest\ClassVariance\SeparatorClassMerger;
+
+/**
+ * Configuration for cv() — separator-based class merging with no Tailwind dependency.
+ *
+ * The group key for each class is everything before the first occurrence of
+ * $separator (default '-'). Within a group, last class wins.
+ *
+ * An optional $classGroups map can declare explicit conflict groups for classes
+ * that share no common prefix (e.g. display utilities: block / flex / hidden).
+ */
+final class GenericClassVarianceConfig implements ClassVarianceConfig
+{
+    public function __construct(
+        public readonly string $separator = '-',
+        public readonly ?Classmap $classGroups = null,
+    ) {}
+
+    public ClassMerger $merger {
+        get => new SeparatorClassMerger($this->separator, $this->classGroups);
+    }
+}
diff --git a/packages/class-variance/src/Config/TailwindClassVarianceConfig.php b/packages/class-variance/src/Config/TailwindClassVarianceConfig.php
new file mode 100644
index 0000000000..05f81a50af
--- /dev/null
+++ b/packages/class-variance/src/Config/TailwindClassVarianceConfig.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Config;
+
+use Tempest\ClassVariance\Classmaps\Classmap;
+use Tempest\ClassVariance\Classmaps\TailwindClassmap;
+use Tempest\ClassVariance\ClassMerger;
+use Tempest\ClassVariance\GroupClassMerger;
+
+/**
+ * Configuration for tv() — Tailwind-aware class merging.
+ *
+ * Ships with the full Tailwind CSS class group definitions and conflict rules
+ * ported from tailwind-merge. Custom plugin utilities or non-standard theme
+ * values can be added via $extend (additive) or $override (replaces a group).
+ *
+ * Use $prefix when your Tailwind config sets a custom class prefix (e.g. 'tw-').
+ * Use $separator when you have changed the variant separator from the default ':'.
+ */
+final class TailwindClassVarianceConfig implements ClassVarianceConfig
+{
+    public function __construct(
+        public readonly string $prefix = '',
+        public readonly string $separator = ':',
+        public readonly ?Classmap $extend = null,
+        public readonly ?Classmap $override = null,
+    ) {}
+
+    public ClassMerger $merger {
+        get {
+            $groups = TailwindClassmap::default();
+
+            $extend = $this->extend;
+            if ($extend instanceof Classmap) {
+                $groups = $groups->extend($extend);
+            }
+
+            $override = $this->override;
+            if ($override instanceof Classmap) {
+                $groups = $groups->override($override);
+            }
+
+            return new GroupClassMerger($groups, $this->prefix, $this->separator);
+        }
+    }
+}
diff --git a/packages/class-variance/src/CvMergerInitializer.php b/packages/class-variance/src/CvMergerInitializer.php
new file mode 100644
index 0000000000..0d6f97ff1b
--- /dev/null
+++ b/packages/class-variance/src/CvMergerInitializer.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+use Tempest\ClassVariance\Config\GenericClassVarianceConfig;
+use Tempest\Container\Container;
+use Tempest\Container\Initializer;
+use Tempest\Container\Singleton;
+
+/**
+ * Registers the cv() ClassMerger (separator-based) as a singleton tagged 'cv'.
+ *
+ * Respects a GenericClassVarianceConfig binding when one is present in the
+ * container, otherwise falls back to the default configuration.
+ *
+ * Inject via: #[Tag('cv')] ClassMerger $merger
+ */
+final readonly class CvMergerInitializer implements Initializer
+{
+    #[Singleton(tag: 'cv')]
+    public function initialize(Container $container): ClassMerger
+    {
+        $config = $container->has(GenericClassVarianceConfig::class)
+            ? $container->get(GenericClassVarianceConfig::class)
+            : new GenericClassVarianceConfig();
+
+        return $config->merger;
+    }
+}
diff --git a/packages/class-variance/src/GenericClassVariance.php b/packages/class-variance/src/GenericClassVariance.php
new file mode 100644
index 0000000000..b8cf975b4f
--- /dev/null
+++ b/packages/class-variance/src/GenericClassVariance.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+/**
+ * The single concrete ClassVariance implementation used by both cv() and tv().
+ * The merger injected at construction time determines the conflict-resolution strategy.
+ */
+final readonly class GenericClassVariance implements ClassVariance
+{
+    use ResolvesVariants;
+
+    /**
+     * @param array<string, string|list<string>|array<string, string|list<string>>>|list<string>|string $base
+     *   Base classes. A plain string or indexed array targets the implicit 'base' slot.
+     *   An associative array is a slot-keyed map: ['base' => '...', 'label' => '...'].
+     * @param array<string, array<string, string|list<string>|array<string, string|list<string>>>> $variants
+     *   Variant dimensions. Keys are prop names; values map prop values to classes.
+     *   Per-value classes may be a plain string (implicit 'base') or a slot-keyed array.
+     * @param array<int, array<string, mixed>> $compoundVariants
+     *   Each entry is a compound rule. All keys except 'class'/'className' are match
+     *   conditions; 'class' holds the classes to apply when all conditions match.
+     * @param array<string, string|bool> $defaultVariants
+     *   Default prop values applied when a prop is not explicitly provided.
+     */
+    public function __construct(
+        public array|string $base,
+        public ClassMerger $merger,
+        public array $variants = [],
+        public array $compoundVariants = [],
+        public array $defaultVariants = [],
+    ) {}
+}
diff --git a/packages/class-variance/src/GroupClassMerger.php b/packages/class-variance/src/GroupClassMerger.php
new file mode 100644
index 0000000000..d0e1ae91ab
--- /dev/null
+++ b/packages/class-variance/src/GroupClassMerger.php
@@ -0,0 +1,119 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+use Tempest\ClassVariance\Classmaps\Classmap;
+
+/**
+ * Merges CSS class strings using a ClassGroupMap for conflict resolution.
+ *
+ * Algorithm (mirrors tailwind-merge):
+ *   1. Strip any Tailwind prefix (e.g. 'tw-') from the base class.
+ *   2. Extract variant modifiers (e.g. 'hover:', 'dark:', 'lg:') from the class.
+ *      Modifiers are separated by $separator (default ':') outside of [] brackets.
+ *   3. Look up the base class in the ClassGroupMap to find its group ID.
+ *   4. The deduplication key is modifier_string + group_id.
+ *   5. When a class is stored, all previously stored classes whose key corresponds
+ *      to a group listed in conflictingClassGroups[group_id] are removed.
+ *   6. Classes whose group is unknown are kept as-is (they cannot conflict).
+ *   7. Last class for each key wins.
+ *
+ * Use this merger via tv() for Tailwind CSS class strings.
+ * For non-Tailwind class strings use SeparatorClassMerger via cv() instead.
+ */
+final readonly class GroupClassMerger implements ClassMerger
+{
+    public function __construct(
+        private Classmap $classGroups,
+        private string $prefix = '',
+        private string $separator = ':',
+    ) {}
+
+    public function merge(string ...$classes): string
+    {
+        /** @var array<string, string> $resolved  key => original class string */
+        $resolved = [];
+
+        foreach ($classes as $class) {
+            if ($class === '') {
+                continue;
+            }
+
+            [$modifiers, $baseClass] = $this->extractModifiers($class);
+
+            $withoutPrefix = $this->stripPrefix($baseClass);
+
+            $groupId = $this->classGroups->findGroup($withoutPrefix);
+
+            if ($groupId === null) {
+                // Unknown class — keep it, keyed by the full string so it is never
+                // displaced by another unknown class that happens to share a name.
+                $resolved['__unknown__' . $class] = $class;
+                continue;
+            }
+
+            $key = $modifiers . ':' . $groupId;
+
+            // Remove classes from groups that conflict with the incoming group.
+            foreach ($this->classGroups->conflictingClassGroups[$groupId] ?? [] as $conflictId) {
+                $conflictKey = $modifiers . ':' . $conflictId;
+                unset($resolved[$conflictKey]);
+            }
+
+            $resolved[$key] = $class;
+        }
+
+        return implode(' ', array_values($resolved));
+    }
+
+    /**
+     * Split a class string into [modifiers, baseClass].
+     * Separators inside [] brackets (arbitrary values) are ignored.
+     *
+     * Example: 'dark:hover:bg-red-500' → ['dark:hover', 'bg-red-500']
+     * Example: 'p-[color:red]'         → ['', 'p-[color:red]']
+     *
+     * @return array{0: string, 1: string}
+     */
+    private function extractModifiers(string $class): array
+    {
+        if ($this->separator === '' || ! str_contains($class, $this->separator)) {
+            return ['', $class];
+        }
+
+        $sepLen = strlen($this->separator);
+        $depth = 0;
+        $lastPos = -1;
+        $len = strlen($class);
+
+        for ($i = 0; $i < $len; $i++) {
+            if ($class[$i] === '[') {
+                $depth++;
+            } elseif ($class[$i] === ']') {
+                $depth--;
+            } elseif ($depth === 0 && substr($class, $i, $sepLen) === $this->separator) {
+                $lastPos = $i;
+            }
+        }
+
+        if ($lastPos === -1) {
+            return ['', $class];
+        }
+
+        return [
+            substr($class, 0, $lastPos),
+            substr($class, $lastPos + $sepLen),
+        ];
+    }
+
+    private function stripPrefix(string $class): string
+    {
+        if ($this->prefix === '' || ! str_starts_with($class, $this->prefix)) {
+            return $class;
+        }
+
+        return substr($class, strlen($this->prefix));
+    }
+}
diff --git a/packages/class-variance/src/ResolvesVariants.php b/packages/class-variance/src/ResolvesVariants.php
new file mode 100644
index 0000000000..29e59b1bba
--- /dev/null
+++ b/packages/class-variance/src/ResolvesVariants.php
@@ -0,0 +1,185 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+use InvalidArgumentException;
+
+/**
+ * Core variant resolution engine, shared by all ClassVariance implementations.
+ *
+ * The class using this trait must declare the following public readable properties:
+ *   - array|string $base
+ *   - ClassMerger  $merger
+ *   - array        $variants
+ *   - array        $compoundVariants
+ *   - array        $defaultVariants
+ *
+ * @property-read array|string $base
+ * @property-read ClassMerger $merger
+ * @property-read array $variants
+ * @property-read array $compoundVariants
+ * @property-read array $defaultVariants
+ *
+ * @internal
+ */
+trait ResolvesVariants
+{
+    /** @param array<string, string|bool|array<string, string|bool>> $props */
+    public function __invoke(array $props = [], string $slot = ''): string
+    {
+        $props = $this->applyDefaultVariants($props);
+        $slot = $this->resolveSlot($slot);
+
+        $classes = ClassNames::of($this->base, $slot)
+            ->concat($this->resolveVariants($props, $slot))
+            ->concat($this->resolveCompoundVariants($props, $slot))
+            ->concat($this->resolvePassthrough($props, $slot));
+
+        return $this->merger->merge(...$classes->toArray());
+    }
+
+    /**
+     * @param array<string, string|bool|array<string, string|bool>> $props
+     * @return array<string, string|bool|array<string, string|bool>>
+     */
+    private function applyDefaultVariants(array $props): array
+    {
+        /** @var array<string, string|bool> $defaults */
+        $defaults = $this->defaultVariants;
+
+        foreach ($defaults as $key => $value) {
+            $props[$key] ??= $value;
+        }
+
+        return $props;
+    }
+
+    private function resolveSlot(string $slot): string
+    {
+        if ($slot !== '') {
+            return $slot;
+        }
+
+        // If base is a slot-keyed associative array, try to infer the slot.
+        if (is_array($this->base) && ! array_is_list($this->base)) {
+            if (count($this->base) === 1) {
+                return (string) array_key_first($this->base);
+            } else {
+                throw new InvalidArgumentException(
+                    'Multiple slots defined but no slot specified. Available slots: ' . implode(', ', array_keys($this->base)),
+                );
+            }
+        }
+
+        return $slot;
+    }
+
+    /**
+     * Resolve the extra classes from $props['class'] or $props['className'].
+     *
+     * Plain strings and indexed arrays always apply to the current slot (passthrough context).
+     * Associative (slot-keyed) arrays are extracted by the current slot name,
+     * matching the same shape used in variant definitions.
+     *
+     * @param array<string, mixed> $props
+     */
+    private function resolvePassthrough(array $props, string $slot): ClassNames
+    {
+        /** @var string|array<array-key, mixed>|bool $value */
+        $value = $props['class'] ?? $props['className'] ?? '';
+
+        if (is_bool($value) || $value === '') {
+            return ClassNames::empty();
+        }
+
+        // Slot-keyed array: extract only the classes for the current slot.
+        if (is_array($value) && ! array_is_list($value)) {
+            return ClassNames::of($value, $slot);
+        }
+
+        // Plain string or indexed list: applies to the current slot unconditionally.
+        return ClassNames::of($value, '');
+    }
+
+    /**
+     * @param array<string, string|bool|array<string, string|bool>> $props
+     */
+    private function resolveVariants(array $props, string $slot): ClassNames
+    {
+        $classes = ClassNames::empty();
+
+        /** @var array<string, array<string, string|array<string, mixed>>> $variants */
+        $variants = $this->variants;
+
+        foreach ($props as $key => $value) {
+            if (is_array($value)) {
+                continue;
+            }
+
+            $lookupKey = match (true) {
+                $value === true => 'true',
+                $value === false => 'false',
+                default => $value,
+            };
+            $entry = $variants[$key][$lookupKey] ?? null;
+
+            if ($entry === null) {
+                continue;
+            }
+
+            $classes = $classes->concat(ClassNames::of($entry, $slot));
+        }
+
+        return $classes;
+    }
+
+    /**
+     * @param array<string, string|bool|array<string, string|bool>> $props
+     */
+    private function resolveCompoundVariants(array $props, string $slot): ClassNames
+    {
+        $classes = ClassNames::empty();
+
+        /** @var array<int, array<string, mixed>> $compoundVariants */
+        $compoundVariants = $this->compoundVariants;
+
+        foreach ($compoundVariants as $compound) {
+            if (! $this->compoundMatches($props, $compound)) {
+                continue;
+            }
+
+            /** @var string|array<string, mixed>|bool $classValue */
+            $classValue = $compound['class'] ?? $compound['className'] ?? '';
+            $classes = $classes->concat(ClassNames::of($classValue, $slot));
+        }
+
+        return $classes;
+    }
+
+    /**
+     * @param array<string, string|bool|array<string, string|bool>> $props
+     * @param array<string, mixed> $compound
+     */
+    private function compoundMatches(array $props, array $compound): bool
+    {
+        foreach ($compound as $key => $value) {
+            if ($key === 'class') {
+                continue;
+            }
+            if ($key === 'className') {
+                continue;
+            }
+            if (is_array($value)) {
+                if (! isset($props[$key]) || ! in_array($props[$key], $value, strict: true)) {
+                    return false;
+                }
+            } elseif (! isset($props[$key]) || $props[$key] !== $value) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}
diff --git a/packages/class-variance/src/SeparatorClassMerger.php b/packages/class-variance/src/SeparatorClassMerger.php
new file mode 100644
index 0000000000..bb32bac844
--- /dev/null
+++ b/packages/class-variance/src/SeparatorClassMerger.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+use Tempest\ClassVariance\Classmaps\Classmap;
+
+/**
+ * Merges CSS class strings using a configurable separator to determine groups.
+ *
+ * The group key for a class is everything before its first occurrence of
+ * $separator (default '-'). Classes with no separator are treated as singleton
+ * groups and do not conflict with anything unless explicitly declared in
+ * $classGroups.
+ *
+ * An optional ClassGroupMap can declare explicit groups (e.g. display utilities
+ * like 'block' / 'flex' / 'hidden' that conflict without sharing a prefix).
+ *
+ * Within each group, last-in wins.
+ *
+ * This merger makes no assumption about Tailwind CSS. Use GroupClassMerger
+ * (via tv()) for full Tailwind-aware conflict resolution.
+ */
+final readonly class SeparatorClassMerger implements ClassMerger
+{
+    public function __construct(
+        private string $separator = '-',
+        private ?Classmap $classGroups = null,
+    ) {}
+
+    public function merge(string ...$classes): string
+    {
+        /** @var array<string, string> $resolved group-key => class */
+        $resolved = [];
+
+        foreach ($classes as $class) {
+            if ($class === '') {
+                continue;
+            }
+
+            $groupKey = $this->resolveGroup($class);
+            $resolved[$groupKey] = $class;
+        }
+
+        return implode(' ', array_values($resolved));
+    }
+
+    private function resolveGroup(string $class): string
+    {
+        // Explicit group map takes priority over separator heuristic.
+        if ($this->classGroups instanceof Classmap) {
+            $group = $this->classGroups->findGroup($class);
+
+            if ($group !== null) {
+                return $group;
+            }
+        }
+
+        $pos = strpos($class, $this->separator);
+
+        if ($pos === false) {
+            // No separator — class is its own group (won't conflict with others).
+            return $class;
+        }
+
+        return substr($class, 0, $pos);
+    }
+}
diff --git a/packages/class-variance/src/TvMergerInitializer.php b/packages/class-variance/src/TvMergerInitializer.php
new file mode 100644
index 0000000000..8085a8ba79
--- /dev/null
+++ b/packages/class-variance/src/TvMergerInitializer.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+use Tempest\ClassVariance\Config\TailwindClassVarianceConfig;
+use Tempest\Container\Container;
+use Tempest\Container\Initializer;
+use Tempest\Container\Singleton;
+
+/**
+ * Registers the tv() ClassMerger (Tailwind-aware) as a singleton tagged 'tv'.
+ *
+ * TailwindClassmap::default() is built once per container lifecycle rather
+ * than on every tv() call.
+ *
+ * Respects a TailwindClassVarianceConfig binding when one is present in the
+ * container (e.g. to supply a custom prefix, separator, or extend/override map),
+ * otherwise falls back to the default configuration.
+ *
+ * Inject via: #[Tag('tv')] ClassMerger $merger
+ */
+final readonly class TvMergerInitializer implements Initializer
+{
+    #[Singleton(tag: 'tv')]
+    public function initialize(Container $container): ClassMerger
+    {
+        $config = $container->has(TailwindClassVarianceConfig::class)
+            ? $container->get(TailwindClassVarianceConfig::class)
+            : new TailwindClassVarianceConfig();
+
+        return $config->merger;
+    }
+}
diff --git a/packages/class-variance/src/functions.php b/packages/class-variance/src/functions.php
new file mode 100644
index 0000000000..adef20fece
--- /dev/null
+++ b/packages/class-variance/src/functions.php
@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance;
+
+use Tempest\ClassVariance\Config\ClassVarianceConfig;
+use Tempest\ClassVariance\Config\GenericClassVarianceConfig;
+use Tempest\ClassVariance\Config\TailwindClassVarianceConfig;
+use Tempest\Container\GenericContainer;
+
+/**
+ * Create a class variance authority with generic (non-Tailwind) merging.
+ *
+ * The default merger splits on '-' and keeps the last class per prefix group.
+ * Pass a ClassGroupMap via GenericClassVarianceConfig to declare explicit
+ * conflict groups for classes that share no common prefix.
+ *
+ * @param array<string, string|list<string>|array<string, string|list<string>>>|list<string>|string $base
+ *   Base classes. A plain string or indexed array implicitly targets the 'base'
+ *   slot. An associative array is a slot-keyed map.
+ * @param array<string, array<string, string|list<string>|array<string, string|list<string>>>> $variants
+ * @param array<int, array<string, mixed>> $compoundVariants
+ * @param array<string, string|bool> $defaultVariants
+ */
+function cv(
+    array|string $base,
+    array $variants = [],
+    array $compoundVariants = [],
+    array $defaultVariants = [],
+    ?ClassVarianceConfig $config = null,
+): ClassVariance {
+    $container = GenericContainer::instance();
+    $config ??= $container?->has(GenericClassVarianceConfig::class)
+        ? $container->get(GenericClassVarianceConfig::class)
+        : new GenericClassVarianceConfig();
+
+    return new GenericClassVariance($base, $config->merger, $variants, $compoundVariants, $defaultVariants);
+}
+
+/**
+ * Create a class variance authority with Tailwind-aware merging.
+ *
+ * Ships with the full Tailwind CSS class group definitions and conflict rules.
+ * Pass a TailwindClassVarianceConfig to extend/override groups for custom
+ * plugins or a non-standard Tailwind prefix / separator.
+ *
+ * @param array<string, string|list<string>|array<string, string|list<string>>>|list<string>|string $base
+ *   Base classes. A plain string or indexed array implicitly targets the 'base'
+ *   slot. An associative array is a slot-keyed map.
+ * @param array<string, array<string, string|list<string>|array<string, string|list<string>>>> $variants
+ * @param array<int, array<string, mixed>> $compoundVariants
+ * @param array<string, string|bool> $defaultVariants
+ */
+function tv(
+    array|string $base,
+    array $variants = [],
+    array $compoundVariants = [],
+    array $defaultVariants = [],
+    ?ClassVarianceConfig $config = null,
+): ClassVariance {
+    $container = GenericContainer::instance();
+    $config ??= $container?->has(TailwindClassVarianceConfig::class)
+        ? $container->get(TailwindClassVarianceConfig::class)
+        : new TailwindClassVarianceConfig();
+
+    return new GenericClassVariance($base, $config->merger, $variants, $compoundVariants, $defaultVariants);
+}
diff --git a/packages/class-variance/tests/ClassNamesBooleanTest.php b/packages/class-variance/tests/ClassNamesBooleanTest.php
new file mode 100644
index 0000000000..2aa02af5d8
--- /dev/null
+++ b/packages/class-variance/tests/ClassNamesBooleanTest.php
@@ -0,0 +1,103 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Tests;
+
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+
+use function Tempest\ClassVariance\tv;
+
+final class ClassNamesBooleanTest extends TestCase
+{
+    #[Test]
+    public function class_prop_with_boolean_value_ignored(): void
+    {
+        $component = tv(
+            base: ['base' => ['component']],
+            variants: [
+                'variant' => [
+                    'primary' => ['base' => 'bg-blue-500'],
+                ],
+            ],
+            defaultVariants: ['variant' => 'primary'],
+        );
+
+        $this->assertSame('component bg-blue-500', $component(['class' => true], 'base'));
+        $this->assertSame('component bg-blue-500', $component(['class' => false], 'base'));
+        $this->assertSame('component bg-blue-500', $component(['className' => true], 'base'));
+        $this->assertSame('component bg-blue-500', $component(['className' => false], 'base'));
+    }
+
+    #[Test]
+    public function class_prop_normal_strings_still_work(): void
+    {
+        $component = tv(
+            base: ['base' => ['component']],
+            variants: [
+                'variant' => [
+                    'primary' => ['base' => 'bg-blue-500'],
+                ],
+            ],
+            defaultVariants: ['variant' => 'primary'],
+        );
+
+        $this->assertSame(
+            'component bg-blue-500 custom-class',
+            $component(['class' => 'custom-class'], 'base'),
+        );
+
+        $this->assertSame(
+            'component bg-blue-500 another-class',
+            $component(['className' => 'another-class'], 'base'),
+        );
+
+        // Two unknown classes with the same prefix: tv() keeps both (unknown classes are never deduplicated)
+        $this->assertSame(
+            'component bg-blue-500 custom-1 custom-2',
+            $component(['class' => 'custom-1 custom-2'], 'base'),
+        );
+    }
+
+    #[Test]
+    public function slot_based_class_with_boolean_in_array(): void
+    {
+        $component = tv(
+            base: [
+                'base' => ['component-base'],
+                'label' => ['component-label'],
+            ],
+            variants: [
+                'variant' => [
+                    'primary' => [
+                        'base' => ['bg-blue-500'],
+                        'label' => ['text-white'],
+                    ],
+                ],
+            ],
+            defaultVariants: ['variant' => 'primary'],
+        );
+
+        // Boolean in slot class array ignored; only the matching slot's value applied
+        $this->assertSame(
+            'component-base bg-blue-500',
+            $component(['class' => ['base' => true, 'label' => 'extra']], 'base'),
+        );
+
+        $this->assertSame(
+            'component-label text-white extra',
+            $component(['class' => ['base' => true, 'label' => 'extra']], 'label'),
+        );
+    }
+
+    #[Test]
+    public function empty_string_and_whitespace_still_filtered(): void
+    {
+        $component = tv(base: ['base' => ['component']]);
+
+        $this->assertSame('component', $component(['class' => ''], 'base'));
+        $this->assertSame('component', $component(['class' => '   '], 'base'));
+        $this->assertSame('component', $component(['class' => false], 'base'));
+    }
+}
diff --git a/packages/class-variance/tests/CompoundVariantsAdvancedTest.php b/packages/class-variance/tests/CompoundVariantsAdvancedTest.php
new file mode 100644
index 0000000000..7d82b07233
--- /dev/null
+++ b/packages/class-variance/tests/CompoundVariantsAdvancedTest.php
@@ -0,0 +1,133 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Tests;
+
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+
+use function Tempest\ClassVariance\tv;
+
+final class CompoundVariantsAdvancedTest extends TestCase
+{
+    #[Test]
+    public function compound_variant_with_array_conditions(): void
+    {
+        $component = tv(
+            base: [
+                'base' => ['component'],
+                'content' => ['content-base'],
+                'leading' => ['leading-base'],
+            ],
+            variants: [
+                'variant' => [
+                    'solid' => ['base' => ['bg-solid']],
+                    'outline' => ['base' => ['border-outline']],
+                    'soft' => ['base' => ['bg-soft']],
+                    'subtle' => ['base' => ['bg-subtle']],
+                ],
+                'compact' => [
+                    'true' => ['content' => ['p-2']],
+                    'false' => ['content' => ['p-4']],
+                ],
+            ],
+            compoundVariants: [
+                [
+                    'variant' => ['solid', 'outline', 'soft', 'subtle'],
+                    'compact' => 'false',
+                    'class' => [
+                        'content' => 'px-4 py-3 rounded-lg min-h-12',
+                        'leading' => 'mt-2',
+                    ],
+                ],
+            ],
+            defaultVariants: [
+                'variant' => 'solid',
+                'compact' => 'false',
+            ],
+        );
+
+        // Default: variant=solid, compact=false — compound matches
+        $this->assertSame(
+            'content-base p-4 px-4 py-3 rounded-lg min-h-12',
+            $component(slot: 'content'),
+        );
+
+        $this->assertSame(
+            'leading-base mt-2',
+            $component(slot: 'leading'),
+        );
+
+        // variant=outline, compact=false — compound still matches
+        $this->assertSame(
+            'content-base p-4 px-4 py-3 rounded-lg min-h-12',
+            $component(['variant' => 'outline', 'compact' => 'false'], 'content'),
+        );
+
+        // variant=solid, compact=true — compound does NOT match
+        $this->assertSame(
+            'content-base p-2',
+            $component(['variant' => 'solid', 'compact' => 'true'], 'content'),
+        );
+    }
+
+    #[Test]
+    public function compound_variant_with_multiple_array_conditions(): void
+    {
+        $component = tv(
+            base: ['base' => ['component']],
+            variants: [
+                'color' => [
+                    'neutral' => ['base' => 'text-neutral'],
+                    'primary' => ['base' => 'text-primary'],
+                ],
+                'variant' => [
+                    'outline' => ['base' => 'border'],
+                    'subtle' => ['base' => 'bg-subtle'],
+                ],
+                'multiple' => [
+                    'true' => ['base' => 'multiple'],
+                    'false' => ['base' => 'single'],
+                ],
+            ],
+            compoundVariants: [
+                [
+                    'color' => 'neutral',
+                    'multiple' => 'true',
+                    'variant' => ['outline', 'subtle'],
+                    'class' => ['base' => 'has-focus-visible:ring-2 has-focus-visible:ring-inverted'],
+                ],
+            ],
+            defaultVariants: [
+                'color' => 'neutral',
+                'variant' => 'outline',
+                'multiple' => 'false',
+            ],
+        );
+
+        // Default: multiple=false — compound does NOT match
+        $this->assertSame(
+            'component text-neutral border single',
+            $component(slot: 'base'),
+        );
+
+        // color=neutral, variant=outline, multiple=true — compound matches
+        $this->assertSame(
+            'component text-neutral border multiple has-focus-visible:ring-2 has-focus-visible:ring-inverted',
+            $component(['color' => 'neutral', 'variant' => 'outline', 'multiple' => 'true'], 'base'),
+        );
+
+        // color=neutral, variant=subtle, multiple=true — compound matches
+        $this->assertSame(
+            'component text-neutral bg-subtle multiple has-focus-visible:ring-2 has-focus-visible:ring-inverted',
+            $component(['color' => 'neutral', 'variant' => 'subtle', 'multiple' => 'true'], 'base'),
+        );
+
+        // color=primary — compound does NOT match
+        $this->assertSame(
+            'component text-primary border multiple',
+            $component(['color' => 'primary', 'variant' => 'outline', 'multiple' => 'true'], 'base'),
+        );
+    }
+}
diff --git a/packages/class-variance/tests/CvTest.php b/packages/class-variance/tests/CvTest.php
new file mode 100644
index 0000000000..edff7d8f1b
--- /dev/null
+++ b/packages/class-variance/tests/CvTest.php
@@ -0,0 +1,109 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Tests;
+
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+
+use function Tempest\ClassVariance\cv;
+use function Tempest\ClassVariance\tv;
+
+final class CvTest extends TestCase
+{
+    #[Test]
+    public function tv_resolves_defaults_and_compound_variants(): void
+    {
+        $button = tv(
+            base: ['font-semibold', 'border', 'rounded'],
+            variants: [
+                'variant' => [
+                    'primary' => ['bg-blue-500', 'text-white', 'border-transparent', 'hover:bg-blue-600'],
+                    'secondary' => ['bg-white', 'text-gray-800', 'border-gray-400', 'hover:bg-gray-100'],
+                ],
+                'size' => [
+                    'small' => ['text-sm', 'py-1', 'px-2'],
+                    'medium' => ['text-base', 'py-2', 'px-4'],
+                ],
+            ],
+            compoundVariants: [
+                [
+                    'variant' => 'primary',
+                    'size' => 'medium',
+                    'class' => 'uppercase',
+                ],
+            ],
+            defaultVariants: [
+                'variant' => 'primary',
+                'size' => 'medium',
+            ],
+        );
+
+        $this->assertSame(
+            'font-semibold border rounded bg-blue-500 text-white border-transparent hover:bg-blue-600 text-base py-2 px-4 uppercase',
+            $button(),
+        );
+
+        $this->assertSame(
+            'font-semibold border rounded bg-white text-gray-800 border-gray-400 hover:bg-gray-100 text-sm py-1 px-2',
+            $button(['variant' => 'secondary', 'size' => 'small']),
+        );
+    }
+
+    #[Test]
+    public function class_prop_appended_and_takes_priority_over_classname(): void
+    {
+        $button = tv(
+            base: ['font-semibold', 'border', 'rounded'],
+            variants: [
+                'variant' => [
+                    'secondary' => ['bg-white', 'text-gray-800', 'border-gray-400', 'hover:bg-gray-100'],
+                ],
+                'size' => [
+                    'small' => ['text-sm', 'py-1', 'px-2'],
+                ],
+            ],
+            defaultVariants: ['variant' => 'secondary', 'size' => 'small'],
+        );
+
+        // When both class and className are provided, class takes priority (className ignored)
+        $this->assertSame(
+            'font-semibold border rounded bg-white text-gray-800 border-gray-400 hover:bg-gray-100 text-sm py-1 px-2 focus:ring-2',
+            $button(['class' => 'focus:ring-2', 'className' => 'focus:ring-4', 'variant' => 'secondary', 'size' => 'small']),
+        );
+
+        // className used when class is absent
+        $this->assertSame(
+            'font-semibold border rounded bg-white text-gray-800 border-gray-400 hover:bg-gray-100 text-sm py-1 px-2 focus:ring-2',
+            $button(['className' => 'focus:ring-2', 'variant' => 'secondary', 'size' => 'small']),
+        );
+    }
+
+    #[Test]
+    public function cv_separator_deduplication(): void
+    {
+        // cv() uses separator heuristic: classes sharing a prefix-before-'-' conflict.
+        // Last class in the group wins — this is the intentional cv() behaviour.
+        $component = cv(
+            base: 'btn',
+            variants: [
+                'size' => [
+                    'sm' => 'size-sm',
+                    'lg' => 'size-lg',
+                ],
+                'intent' => [
+                    'primary' => 'intent-primary',
+                    'danger' => 'intent-danger',
+                ],
+            ],
+            defaultVariants: ['size' => 'sm', 'intent' => 'primary'],
+        );
+
+        $this->assertSame('btn size-sm intent-primary', $component());
+        $this->assertSame('btn size-lg intent-danger', $component(['size' => 'lg', 'intent' => 'danger']));
+
+        // Passing class= with a class that shares prefix with a base class: last wins
+        $this->assertSame('btn size-lg intent-primary', $component(['class' => 'size-lg']));
+    }
+}
diff --git a/packages/class-variance/tests/CvWithSlotTest.php b/packages/class-variance/tests/CvWithSlotTest.php
new file mode 100644
index 0000000000..b1f659b4aa
--- /dev/null
+++ b/packages/class-variance/tests/CvWithSlotTest.php
@@ -0,0 +1,168 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\ClassVariance\Tests;
+
+use InvalidArgumentException;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+
+use function Tempest\ClassVariance\cv;
+use function Tempest\ClassVariance\tv;
+
+final class CvWithSlotTest extends TestCase
+{
+    #[Test]
+    public function tv_resolves_slots_with_variants_and_compound_variants(): void
+    {
+        $button = tv(
+            base: [
+                'base' => ['font-semibold', 'border', 'rounded'],
+                'label' => [''],
+            ],
+            variants: [
+                'color' => [
+                    'primary' => [
+                        'base' => ['bg-blue-500', 'border-transparent', 'hover:bg-blue-600'],
+                        'label' => ['text-white'],
+                    ],
+                    'secondary' => [
+                        'base' => ['bg-white', 'border-gray-400', 'hover:bg-gray-100'],
+                        'label' => ['text-black'],
+                    ],
+                ],
+                'size' => [
+                    'small' => [
+                        'base' => ['py-1', 'px-2'],
+                        'label' => ['text-sm'],
+                    ],
+                    'medium' => [
+                        'base' => ['py-2', 'px-4'],
+                        'label' => ['text-base'],
+                    ],
+                ],
+            ],
+            compoundVariants: [
+                [
+                    'color' => 'primary',
+                    'size' => 'medium',
+                    'class' => ['label' => 'uppercase'],
+                ],
+            ],
+            defaultVariants: [
+                'color' => 'primary',
+                'size' => 'medium',
+            ],
+        );
+
+        $this->assertSame(
+            'font-semibold border rounded bg-blue-500 border-transparent hover:bg-blue-600 py-2 px-4',
+            $button(slot: 'base'),
+        );
+
+        $this->assertSame(
+            'text-white text-base uppercase',
+            $button(slot: 'label'),
+        );
+
+        $this->assertSame(
+            'font-semibold border rounded bg-white border-gray-400 hover:bg-gray-100 py-1 px-2',
+            $button(props: ['color' => 'secondary', 'size' => 'small'], slot: 'base'),
+        );
+
+        $this->assertSame(
+            'text-black text-sm',
+            $button(props: ['color' => 'secondary', 'size' => 'small'], slot: 'label'),
+        );
+
+        // class takes priority over className for the requested slot
+        $this->assertSame(
+            'font-semibold border rounded bg-white border-gray-400 hover:bg-gray-100 py-1 px-2 focus:ring-2',
+            $button(props: ['class' => 'focus:ring-2', 'className' => 'focus:ring-4', 'color' => 'secondary', 'size' => 'small'], slot: 'base'),
+        );
+
+        $this->assertSame(
+            'font-semibold border rounded bg-white border-gray-400 hover:bg-gray-100 py-1 px-2 focus:ring-2',
+            $button(props: ['className' => 'focus:ring-2', 'color' => 'secondary', 'size' => 'small'], slot: 'base'),
+        );
+
+        // Unknown slot returns empty string
+        $this->assertSame('', $button(slot: 'fooBarBaz'));
+    }
+
+    #[Test]
+    public function implicit_slot_inference_for_single_slot_base(): void
+    {
+        $component = tv(base: ['base' => 'rounded bg-white']);
+
+        // No slot argument — single slot inferred automatically
+        $this->assertSame('rounded bg-white', $component());
+    }
+
+    #[Test]
+    public function plain_string_base_targets_base_slot(): void
+    {
+        $component = tv(
+            base: 'font-bold text-sm',
+            variants: ['size' => ['lg' => 'text-lg']],
+        );
+
+        // tv() is Tailwind-aware: text-sm and text-lg conflict (both font-size group), text-lg wins
+        $this->assertSame('font-bold text-lg', $component(['size' => 'lg'], 'base'));
+        $this->assertSame('font-bold text-lg', $component(['size' => 'lg']));
+        // Non-base slot returns empty for plain-string base
+        $this->assertSame('', $component(['size' => 'lg'], 'label'));
+    }
+
+    #[Test]
+    public function multi_slot_base_without_slot_throws(): void
+    {
+        $component = cv(base: ['base' => 'a', 'label' => 'b']);
+
+        $this->expectException(InvalidArgumentException::class);
+        $component(); // no slot — ambiguous
+    }
+
+    #[Test]
+    public function plain_string_variant_value_implicitly_targets_base_slot(): void
+    {
+        $component = tv(
+            base: [
+                'base' => 'component',
+                'label' => 'label-base',
+            ],
+            variants: [
+                'size' => [
+                    // plain string — implicit base
+                    'sm' => 'text-sm',
+                    // explicit slot map
+                    'lg' => ['base' => 'text-lg', 'label' => 'text-lg-label'],
+                ],
+            ],
+        );
+
+        // Plain 'sm' string only affects base slot
+        $this->assertSame('component text-sm', $component(['size' => 'sm'], 'base'));
+        $this->assertSame('label-base', $component(['size' => 'sm'], 'label'));
+
+        // Explicit slot map affects both slots
+        $this->assertSame('component text-lg', $component(['size' => 'lg'], 'base'));
+        $this->assertSame('label-base text-lg-label', $component(['size' => 'lg'], 'label'));
+    }
+
+    #[Test]
+    public function cv_plain_string_base_targets_base_slot(): void
+    {
+        // cv() with non-Tailwind class names — separator heuristic only
+        $component = cv(
+            base: 'btn size-base',
+            variants: ['size' => ['lg' => 'size-lg']],
+        );
+
+        // size-base and size-lg share 'size' prefix → size-lg replaces size-base
+        $this->assertSame('btn size-lg', $component(['size' => 'lg'], 'base'));
+        // Non-base slot returns empty for plain-string base
+        $this->assertSame('', $component(['size' => 'lg'], 'label'));
+    }
+}