diff --git a/src/Integrations/Divi/Design/ThemeOptionBook.php b/src/Integrations/Divi/Design/ThemeOptionBook.php
new file mode 100644
index 0000000..32d2c26
--- /dev/null
+++ b/src/Integrations/Divi/Design/ThemeOptionBook.php
@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations\Divi\Design;
+
+use InvalidArgumentException;
+use LIT\MCP\Abilities\Rev;
+
+defined('ABSPATH') || exit;
+
+/**
+ * The managed theme options as stored in get_option('et_divi') (ruling W6): only the whitelist keys that are
+ * set, in the fixed order of ThemeOptionSpec::KEYS, with the raw value and type (int, float, string or false –
+ * Divi stores its default font as false). A key that is not set is missing. Takes a snapshot or the whole et_divi
+ * array alike. Immutable – with() and without() return a new book, and a key is either set or missing, never both.
+ * rev() is the design_rev of the area "theme_options". Pure PHP.
+ */
+final class ThemeOptionBook
+{
+    /** 1.0 and 1 are different stored values, so the hash must tell them apart (zero fraction kept). */
+    private const JSON_FLAGS = JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_PRESERVE_ZERO_FRACTION;
+
+    /** @param array<string, int|float|string|false> $data */
+    private function __construct(private array $data)
+    {
+    }
+
+    /** @param array<array-key, mixed> $raw Other keys, null and values of other types are dropped. */
+    public static function fromDivi(array $raw): self
+    {
+        $data = [];
+        foreach (ThemeOptionSpec::KEYS as $key) {
+            $value = $raw[$key] ?? null;
+            if ($value === false || is_int($value) || is_float($value) || is_string($value)) {
+                $data[$key] = $value;
+            }
+        }
+
+        return new self($data);
+    }
+
+    /** @return array<string, int|float|string|false> */
+    public function data(): array
+    {
+        return $this->data;
+    }
+
+    /** Hash of the canonical JSON; the key order is fixed, and 1, 1.0 and "1" differ. */
+    public function rev(): string
+    {
+        // phpcs:ignore WordPress.WP.AlternativeFunctions.json_encode_json_encode -- pure PHP (spec §4.4).
+        $json = (string) json_encode($this->data, self::JSON_FLAGS);
+
+        return Rev::of('theme_options' . "\0" . $json);
+    }
+
+    public function has(string $key): bool
+    {
+        return array_key_exists($key, $this->data);
+    }
+
+    public function get(string $key): int|float|string|false|null
+    {
+        return $this->data[$key] ?? null;
+    }
+
+    /** @throws InvalidArgumentException For a key outside the whitelist. */
+    public function with(string $key, int|float|string|false $value): self
+    {
+        ThemeOptionSpec::definition($key);
+
+        return self::fromDivi([...$this->data, $key => $value]);
+    }
+
+    public function without(string $key): self
+    {
+        return self::fromDivi(array_diff_key($this->data, [$key => true]));
+    }
+}
diff --git a/tests/Unit/Integrations/Divi/Design/ThemeOptionBookTest.php b/tests/Unit/Integrations/Divi/Design/ThemeOptionBookTest.php
new file mode 100644
index 0000000..f036213
--- /dev/null
+++ b/tests/Unit/Integrations/Divi/Design/ThemeOptionBookTest.php
@@ -0,0 +1,115 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Unit\Integrations\Divi\Design;
+
+use InvalidArgumentException;
+use LIT\MCP\Integrations\Divi\Design\ThemeOptionBook;
+use PHPUnit\Framework\TestCase;
+
+final class ThemeOptionBookTest extends TestCase
+{
+    /** @return array<string, mixed> The shape of get_option('et_divi') with the options of other areas around. */
+    public static function stored(): array
+    {
+        return [
+            'accent_color' => '#2ea3f2',
+            'body_font_size' => 16,
+            'heading_font' => false,
+            'logo' => 'https://example.test/logo.png',
+            'body_font_height' => 1.7,
+            'body_header_style' => 'uppercase',
+            'body_font' => 'Lato',
+        ];
+    }
+
+    public function testOnlyWhitelistKeysStayInTheFixedOrderWithTheirRawTypes(): void
+    {
+        $book = ThemeOptionBook::fromDivi(self::stored());
+
+        self::assertSame([
+            'heading_font' => false,
+            'body_font' => 'Lato',
+            'body_font_size' => 16,
+            'body_font_height' => 1.7,
+            'body_header_style' => 'uppercase',
+        ], $book->data());
+        self::assertSame(['heading_font', 'body_font', 'body_font_size', 'body_font_height', 'body_header_style'],
+            array_keys($book->data()));
+    }
+
+    public function testNullAndValuesOfOtherTypesAreDropped(): void
+    {
+        $book = ThemeOptionBook::fromDivi([
+            'heading_font' => null, 'body_font' => ['Lato'], 'content_width' => true, 'row_padding' => 0,
+            'gutter_width' => '3', 'section_padding' => 0.0, 'body_header_spacing' => new \stdClass(),
+        ]);
+
+        self::assertSame(['gutter_width' => '3', 'section_padding' => 0.0, 'row_padding' => 0], $book->data());
+        self::assertSame([], ThemeOptionBook::fromDivi([])->data());
+    }
+
+    public function testHasAndGetDistinguishAFalseValueFromAMissingKey(): void
+    {
+        $book = ThemeOptionBook::fromDivi(self::stored());
+
+        self::assertTrue($book->has('heading_font'));
+        self::assertFalse($book->get('heading_font'));
+        self::assertFalse($book->has('primary_nav_font'));
+        self::assertNull($book->get('primary_nav_font'));
+        self::assertFalse($book->has('logo'));
+        self::assertNull($book->get('logo'));
+        self::assertSame(16, $book->get('body_font_size'));
+    }
+
+    public function testRevIgnoresTheOrderAndOtherKeysButNotValuesOrTheirTypes(): void
+    {
+        $book = ThemeOptionBook::fromDivi(self::stored());
+        $shuffled = ThemeOptionBook::fromDivi(array_reverse(self::stored(), true) + ['phone_body_font_size' => null]);
+
+        self::assertMatchesRegularExpression('/^[0-9a-f]{12}$/', $book->rev());
+        self::assertSame($book->rev(), $shuffled->rev());
+        self::assertSame($book->rev(), ThemeOptionBook::fromDivi($book->data())->rev());
+        self::assertNotSame($book->rev(), $book->with('body_font_size', 17)->rev());
+        self::assertNotSame($book->rev(), $book->with('body_font_size', '16')->rev(), '16 versus "16"');
+        self::assertNotSame($book->rev(), $book->with('heading_font', 'Lato')->rev(), 'false versus a font');
+        self::assertNotSame($book->rev(), $book->without('body_font_size')->rev());
+        self::assertNotSame(
+            ThemeOptionBook::fromDivi(['body_header_height' => 1])->rev(),
+            ThemeOptionBook::fromDivi(['body_header_height' => 1.0])->rev(),
+            '1 versus 1.0'
+        );
+        self::assertNotSame($book->rev(), ThemeOptionBook::fromDivi([])->rev());
+    }
+
+    public function testWithAddsOrReplacesInPlaceOfTheFixedOrderAndLeavesTheOriginalAlone(): void
+    {
+        $book = ThemeOptionBook::fromDivi(self::stored());
+        $changed = $book->with('primary_nav_font', 'Roboto')->with('body_font_size', 18);
+
+        self::assertSame(['heading_font', 'body_font', 'primary_nav_font', 'body_font_size', 'body_font_height',
+            'body_header_style'], array_keys($changed->data()));
+        self::assertSame(18, $changed->get('body_font_size'));
+        self::assertSame(16, $book->get('body_font_size'));
+        self::assertFalse($book->has('primary_nav_font'));
+        self::assertFalse($book->with('body_font', false)->get('body_font'));
+    }
+
+    public function testWithRejectsAKeyOutsideTheWhitelist(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        ThemeOptionBook::fromDivi([])->with('accent_color', '#fff');
+    }
+
+    public function testWithoutRemovesAKeyAndIgnoresAMissingOne(): void
+    {
+        $book = ThemeOptionBook::fromDivi(self::stored());
+        $without = $book->without('heading_font');
+
+        self::assertFalse($without->has('heading_font'));
+        self::assertTrue($book->has('heading_font'));
+        self::assertSame($book->rev(), $book->without('row_padding')->rev());
+        self::assertSame($book->data(), $book->without('logo')->data());
+    }
+}