diff --git a/.horde.yml b/.horde.yml
index 197e6b5..2b70b1d 100644
--- a/.horde.yml
+++ b/.horde.yml
@@ -32,3 +32,8 @@ dependencies:
 nocommands:
   - bin/demo-client.php
 vendor: horde
+keywords: []
+
+quality:
+  phpstan:
+    level: 5
diff --git a/src/ConfigFormatterInterface.php b/src/ConfigFormatterInterface.php
new file mode 100644
index 0000000..89eb9a6
--- /dev/null
+++ b/src/ConfigFormatterInterface.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Copyright 2013-2026 The Horde Project (http://www.horde.org/)
+ *
+ * See the enclosed file LICENSE for license information (LGPL). If you
+ * did not receive this file, see http://www.horde.org/licenses/lgpl21.
+ */
+
+namespace Horde\PhpConfigFile;
+
+/**
+ * Interface for configuration file formatters
+ *
+ * Formatters convert configuration arrays into PHP code strings.
+ */
+interface ConfigFormatterInterface
+{
+    /**
+     * Format a configuration array into PHP code string
+     *
+     * @param array<string, mixed> $config Configuration data to format
+     * @return string PHP code (without opening <?php tag)
+     */
+    public function format(array $config): string;
+}
diff --git a/src/Formatter/ClassicHordeFormatter.php b/src/Formatter/ClassicHordeFormatter.php
new file mode 100644
index 0000000..fefbd53
--- /dev/null
+++ b/src/Formatter/ClassicHordeFormatter.php
@@ -0,0 +1,142 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Copyright 2013-2026 The Horde Project (http://www.horde.org/)
+ *
+ * See the enclosed file LICENSE for license information (LGPL). If you
+ * did not receive this file, see http://www.horde.org/licenses/lgpl21.
+ */
+
+namespace Horde\PhpConfigFile\Formatter;
+
+use Horde\PhpConfigFile\ConfigFormatterInterface;
+use Horde\PhpConfigFile\LiteralCode;
+use InvalidArgumentException;
+
+use function is_array;
+use function is_bool;
+use function is_int;
+use function is_float;
+use function is_string;
+use function ksort;
+use function addslashes;
+use function array_shift;
+use function get_debug_type;
+
+/**
+ * Classic Horde config formatter
+ *
+ * Outputs configuration in classic Horde format:
+ * $conf['key1']['key2'] = 'value';
+ *
+ * Features:
+ * - Alphabetical key sorting for deterministic output
+ * - Numeric keys unquoted: $var[0] not $var['0']
+ * - LiteralCode support for constants and expressions
+ * - Empty arrays produce no output
+ * - Only scalar values and LiteralCode supported at leaf level
+ */
+class ClassicHordeFormatter implements ConfigFormatterInterface
+{
+    public function format(array $config): string
+    {
+        // Sort root keys alphabetically
+        ksort($config);
+
+        $output = '';
+        foreach ($config as $rootKey => $value) {
+            $output .= $this->formatValue($rootKey, [], $value);
+        }
+        return $output;
+    }
+
+    /**
+     * Recursively format a value into classic Horde notation
+     *
+     * @param string|int $currentKey Current key being processed
+     * @param array<string|int> $keyPath Path of keys leading to this point
+     * @param mixed $value Value to format
+     * @return string Formatted PHP code lines
+     */
+    private function formatValue(string|int $currentKey, array $keyPath, mixed $value): string
+    {
+        $keyPath[] = $currentKey;
+
+        if (is_array($value)) {
+            // Sort keys alphabetically for deterministic output
+            ksort($value);
+
+            // Recursively process nested arrays
+            $output = '';
+            foreach ($value as $subKey => $subValue) {
+                $output .= $this->formatValue($subKey, $keyPath, $subValue);
+            }
+            return $output;
+        }
+
+        // Leaf value - generate assignment statement
+        return $this->formatLeafAssignment($keyPath, $value);
+    }
+
+    /**
+     * Format a leaf assignment: $var['key1'][2]['key3'] = value;
+     *
+     * @param array<string|int> $keyPath Full path of keys
+     * @param mixed $value Leaf value (scalar or LiteralCode)
+     * @return string Formatted assignment statement
+     */
+    private function formatLeafAssignment(array $keyPath, mixed $value): string
+    {
+        // Build $var['key1'][2]['key3']...
+        $varPath = '$' . array_shift($keyPath);
+        foreach ($keyPath as $key) {
+            if (is_int($key)) {
+                // Numeric keys unquoted
+                $varPath .= "[{$key}]";
+            } else {
+                // String keys quoted and escaped
+                $varPath .= "['" . addslashes((string) $key) . "']";
+            }
+        }
+
+        // Format value based on type
+        $formattedValue = $this->formatScalar($value);
+
+        return "{$varPath} = {$formattedValue};\n";
+    }
+
+    /**
+     * Format a scalar value for PHP output
+     *
+     * @param mixed $value Value to format
+     * @return string Formatted value representation
+     * @throws InvalidArgumentException If value is not scalar or LiteralCode
+     */
+    private function formatScalar(mixed $value): string
+    {
+        // Handle literal code expressions
+        if ($value instanceof LiteralCode) {
+            return $value->getCode();
+        }
+
+        if (is_bool($value)) {
+            return $value ? 'true' : 'false';
+        }
+        if (is_int($value) || is_float($value)) {
+            return (string) $value;
+        }
+        if (is_string($value)) {
+            return "'" . addslashes($value) . "'";
+        }
+        if ($value === null) {
+            return 'null';
+        }
+
+        // Reject non-scalar values
+        throw new InvalidArgumentException(
+            'Only scalar values and LiteralCode are supported. Got: ' . get_debug_type($value)
+        );
+    }
+}
diff --git a/src/Formatter/ModernArrayFormatter.php b/src/Formatter/ModernArrayFormatter.php
new file mode 100644
index 0000000..3345286
--- /dev/null
+++ b/src/Formatter/ModernArrayFormatter.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Copyright 2013-2026 The Horde Project (http://www.horde.org/)
+ *
+ * See the enclosed file LICENSE for license information (LGPL). If you
+ * did not receive this file, see http://www.horde.org/licenses/lgpl21.
+ */
+
+namespace Horde\PhpConfigFile\Formatter;
+
+use Horde\PhpConfigFile\ConfigFormatterInterface;
+
+use function var_export;
+use function is_array;
+
+/**
+ * Modern PHP array formatter using var_export()
+ *
+ * Outputs configuration as modern PHP array syntax:
+ * $config = ['key' => 'value'];
+ *
+ * This is the default formatter, maintaining backward compatibility
+ * with the original PhpConfigFile behavior.
+ */
+class ModernArrayFormatter implements ConfigFormatterInterface
+{
+    public function format(array $config): string
+    {
+        $output = '';
+        foreach ($config as $key => $value) {
+            if (is_array($value)) {
+                $output .= '$' . $key . ' = ' . var_export($value, true) . ";\n";
+            } else {
+                // Scalar values as string (original behavior)
+                $output .= '$' . $key . " = '" . $value . "';\n";
+            }
+        }
+        return $output;
+    }
+}
diff --git a/src/LiteralCode.php b/src/LiteralCode.php
new file mode 100644
index 0000000..72583fc
--- /dev/null
+++ b/src/LiteralCode.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Copyright 2013-2026 The Horde Project (http://www.horde.org/)
+ *
+ * See the enclosed file LICENSE for license information (LGPL). If you
+ * did not receive this file, see http://www.horde.org/licenses/lgpl21.
+ */
+
+namespace Horde\PhpConfigFile;
+
+use Stringable;
+
+/**
+ * Wrapper for literal PHP code expressions that should be output as-is
+ *
+ * Use this when you need to output PHP constants, class constants, or other
+ * expressions that shouldn't be quoted or escaped.
+ *
+ * @example
+ * $config = [
+ *     'conf' => [
+ *         'log_level' => new LiteralCode('Horde_Log::DEBUG'),
+ *         'timeout' => new LiteralCode('60 * 60'), // 1 hour
+ *     ],
+ * ];
+ * // Output: $conf['log_level'] = Horde_Log::DEBUG;
+ * //         $conf['timeout'] = 60 * 60;
+ */
+final readonly class LiteralCode implements Stringable
+{
+    public function __construct(
+        private string $code,
+    ) {}
+
+    public function __toString(): string
+    {
+        return $this->code;
+    }
+
+    public function getCode(): string
+    {
+        return $this->code;
+    }
+}
diff --git a/src/PhpConfigFile.php b/src/PhpConfigFile.php
index 3bc2488..4a8de02 100644
--- a/src/PhpConfigFile.php
+++ b/src/PhpConfigFile.php
@@ -4,6 +4,7 @@
 
 namespace Horde\PhpConfigFile;
 
+use Horde\PhpConfigFile\Formatter\ModernArrayFormatter;
 use Stringable;
 use RuntimeException;
 use InvalidArgumentException;
@@ -18,7 +19,6 @@
 use function trim;
 use function ltrim;
 use function get_defined_vars;
-use function var_export;
 use function in_array;
 
 /**
@@ -32,12 +32,16 @@ class PhpConfigFile
     private string $contentBetweenHeaderAndFooter = '';
     private string $content = '';
     private string $untrustedContent = '';
+    private ?ConfigFormatterInterface $defaultFormatter = null;
 
     public function __construct(
         public readonly string|Stringable $configFilePath,
         public readonly string|Stringable $header = '/* This file is auto-generated. Do not edit anything below this line! */',
         public readonly string|Stringable $footer = '/* This file is auto-generated. Do not edit anything above this line! */',
-    ) {}
+        ?ConfigFormatterInterface $formatter = null,
+    ) {
+        $this->defaultFormatter = $formatter;
+    }
 
     public function getContent(): string
     {
@@ -119,10 +123,10 @@ public function parseContent(string $area = 'content'): array
             // Set up safe defaults for CLI context to prevent undefined key warnings
             if (PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg') {
                 // Preserve existing $_SERVER values but provide safe defaults for missing keys
-                $_SERVER['SERVER_NAME'] = $_SERVER['SERVER_NAME'] ?? 'localhost';
-                $_SERVER['HTTP_HOST'] = $_SERVER['HTTP_HOST'] ?? 'localhost';
-                $_SERVER['REQUEST_URI'] = $_SERVER['REQUEST_URI'] ?? '/';
-                $_SERVER['REMOTE_ADDR'] = $_SERVER['REMOTE_ADDR'] ?? '127.0.0.1';
+                $_SERVER['SERVER_NAME'] ??= 'localhost';
+                $_SERVER['HTTP_HOST'] ??= 'localhost';
+                $_SERVER['REQUEST_URI'] ??= '/';
+                $_SERVER['REMOTE_ADDR'] ??= '127.0.0.1';
             }
 
             eval($this->untrustedContent);
@@ -136,25 +140,25 @@ public function parseContent(string $area = 'content'): array
     /**
      * Write the config file with the given array
      * @param array<mixed> $config The config array to write
+     * @param ConfigFormatterInterface|null $formatter Optional formatter override
      * @return self
      */
-    public function writeConfigFile(array $config): self
+    public function writeConfigFile(array $config, ?ConfigFormatterInterface $formatter = null): self
     {
+        // Determine which formatter to use (priority: parameter > constructor > default)
+        $activeFormatter = $formatter
+            ?? $this->defaultFormatter
+            ?? new ModernArrayFormatter();
+
         // Convert the array back to a string
-        $configContent = "<?php\n" .
-        $this->contentBeforeHeader . "\n" .
-        $this->header . "\n";
-        foreach ($config as $key => $value) {
-            if (is_array($value)) {
-                $configContent .= '$' . $key . ' = ' . var_export($value, true) . ";\n";
-            } else {
-                $configContent .= '$' . $key . ' = \'' . $value . "';\n";
-            }
-        }
-        $configContent .= "\n" .
+        $configContent = "<?php\n"
+        . $this->contentBeforeHeader . "\n"
+        . $this->header . "\n"
+        . $activeFormatter->format($config)
+        . "\n"
+        . $this->footer . "\n"
+        . $this->contentAfterFooter;
 
-        $this->footer . "\n" .
-        $this->contentAfterFooter;
         // Write the content back to the file
         file_put_contents((string) $this->configFilePath, $configContent);
         return $this;
diff --git a/test/fixtures/ClassicHordeFormat.php b/test/fixtures/ClassicHordeFormat.php
index a17d26d..8a6d17b 100644
--- a/test/fixtures/ClassicHordeFormat.php
+++ b/test/fixtures/ClassicHordeFormat.php
@@ -1,7 +1,8 @@
 <?php
+
 /* Horde Begin */
 $conf['sql']['hostspec'] = 'localhost';
 $conf['sql']['username'] = 'horde';
 $conf['sql']['password'] = 'horde';
 $conf['readwritesplit'] = true;
-/* Horde End */
\ No newline at end of file
+/* Horde End */
diff --git a/test/fixtures/NestedModernArrayFormat.php b/test/fixtures/NestedModernArrayFormat.php
index 3f3e974..55a1e0f 100644
--- a/test/fixtures/NestedModernArrayFormat.php
+++ b/test/fixtures/NestedModernArrayFormat.php
@@ -10,4 +10,4 @@
             'subsubkey2' => 'subsubvalue2',
         ],
     ],
-];
\ No newline at end of file
+];
diff --git a/test/fixtures/WithPreHeaderAndPostFooterContent.php b/test/fixtures/WithPreHeaderAndPostFooterContent.php
index f0bd150..93039f4 100644
--- a/test/fixtures/WithPreHeaderAndPostFooterContent.php
+++ b/test/fixtures/WithPreHeaderAndPostFooterContent.php
@@ -13,5 +13,3 @@
 // Values after the footer overwrite managed content in 'content' mode. In 'contentBetweenHeaderAndFooter' mode, these vars are ignored altogether.
 $something = 'overwritten';
 $footer_only = 'footer only';
-
-?>
\ No newline at end of file
diff --git a/test/unit/ConfigurationSchemaTest.php b/test/unit/ConfigurationSchemaTest.php
index e218aed..a08978f 100644
--- a/test/unit/ConfigurationSchemaTest.php
+++ b/test/unit/ConfigurationSchemaTest.php
@@ -10,6 +10,7 @@
 use Horde\PhpConfigFile\StringElement;
 use Horde\PhpConfigFile\IntegerElement;
 use PHPUnit\Framework\Attributes\CoversNothing;
+
 #[CoversNothing]
 class ConfigurationSchemaTest extends TestCase
 {
@@ -37,4 +38,4 @@ public function testConfigurationSchemaWithElements(): void
         $this->assertInstanceOf(IntegerElement::class, $element2, 'Element2 should be an IntegerElement');
         $this->assertEquals(42, $element2->getValue(), 'Element2 value should match');
     }
-}
\ No newline at end of file
+}
diff --git a/test/unit/Formatter/ClassicHordeFormatterTest.php b/test/unit/Formatter/ClassicHordeFormatterTest.php
new file mode 100644
index 0000000..2fd1e35
--- /dev/null
+++ b/test/unit/Formatter/ClassicHordeFormatterTest.php
@@ -0,0 +1,271 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Horde\PhpConfigFile\Test\Unit\Formatter;
+
+use Horde\PhpConfigFile\Formatter\ClassicHordeFormatter;
+use Horde\PhpConfigFile\LiteralCode;
+use InvalidArgumentException;
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use stdClass;
+
+use function strpos;
+
+#[CoversClass(ClassicHordeFormatter::class)]
+class ClassicHordeFormatterTest extends TestCase
+{
+    public function testFormatSimpleString(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key' => 'value']]);
+        $this->assertStringContainsString("\$conf['key'] = 'value';", $result);
+    }
+
+    public function testFormatNestedArray(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $config = ['conf' => ['sql' => ['host' => 'localhost']]];
+        $result = $formatter->format($config);
+        $this->assertStringContainsString("\$conf['sql']['host'] = 'localhost';", $result);
+    }
+
+    public function testFormatBoolean(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['enabled' => true, 'disabled' => false]]);
+        $this->assertStringContainsString("\$conf['enabled'] = true;", $result);
+        $this->assertStringContainsString("\$conf['disabled'] = false;", $result);
+    }
+
+    public function testFormatInteger(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['port' => 3306]]);
+        $this->assertStringContainsString("\$conf['port'] = 3306;", $result);
+    }
+
+    public function testFormatFloat(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['ratio' => 1.5]]);
+        $this->assertStringContainsString("\$conf['ratio'] = 1.5;", $result);
+    }
+
+    public function testFormatNull(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['nullable' => null]]);
+        $this->assertStringContainsString("\$conf['nullable'] = null;", $result);
+    }
+
+    public function testFormatLiteralCode(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['log_level' => new LiteralCode('Horde_Log::DEBUG')]]);
+        $this->assertStringContainsString("\$conf['log_level'] = Horde_Log::DEBUG;", $result);
+    }
+
+    public function testFormatLiteralCodeExpression(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['timeout' => new LiteralCode('60 * 60')]]);
+        $this->assertStringContainsString("\$conf['timeout'] = 60 * 60;", $result);
+    }
+
+    public function testNumericKeysUnquoted(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['items' => [0 => 'first', 1 => 'second']]);
+        $this->assertStringContainsString("\$items[0] = 'first';", $result);
+        $this->assertStringContainsString("\$items[1] = 'second';", $result);
+        $this->assertStringNotContainsString("['0']", $result);
+        $this->assertStringNotContainsString("['1']", $result);
+    }
+
+    public function testEscapesQuotesInKeys(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ["key'with'quotes" => 'value']]);
+        $this->assertStringContainsString("key\\'with\\'quotes", $result);
+    }
+
+    public function testEscapesQuotesInValues(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key' => "val'ue"]]);
+        $this->assertStringContainsString("val\\'ue", $result);
+    }
+
+    public function testEscapesBackslashesInValues(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['path' => 'C:\\Windows\\System']]);
+        $this->assertStringContainsString("C:\\\\Windows\\\\System", $result);
+    }
+
+    public function testAlphabeticalKeyOrdering(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $config = ['conf' => ['z' => 'last', 'a' => 'first', 'm' => 'middle']];
+        $result = $formatter->format($config);
+
+        // Extract line positions
+        $posA = strpos($result, "\$conf['a']");
+        $posM = strpos($result, "\$conf['m']");
+        $posZ = strpos($result, "\$conf['z']");
+
+        $this->assertLessThan($posM, $posA, 'Key "a" should come before "m"');
+        $this->assertLessThan($posZ, $posM, 'Key "m" should come before "z"');
+    }
+
+    public function testAlphabeticalKeyOrderingNested(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $config = ['conf' => ['section' => ['z' => 'last', 'a' => 'first']]];
+        $result = $formatter->format($config);
+
+        $posA = strpos($result, "\$conf['section']['a']");
+        $posZ = strpos($result, "\$conf['section']['z']");
+
+        $this->assertLessThan($posZ, $posA, 'Nested key "a" should come before "z"');
+    }
+
+    public function testEmptyArrayProducesNoOutput(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['empty' => []]]);
+        $this->assertStringNotContainsString('empty', $result, 'Empty arrays should produce no output');
+        $this->assertEquals('', $result);
+    }
+
+    public function testNestedEmptyArraysProduceNoOutput(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['section' => ['subsection' => []]]]);
+        $this->assertEquals('', $result);
+    }
+
+    public function testThrowsExceptionForNonScalarLeafValue(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Only scalar values and LiteralCode are supported');
+
+        $formatter = new ClassicHordeFormatter();
+        $formatter->format(['conf' => ['object' => new stdClass()]]);
+    }
+
+    public function testDeepNesting(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $config = ['conf' => ['l1' => ['l2' => ['l3' => ['l4' => 'deep']]]]];
+        $result = $formatter->format($config);
+        $this->assertStringContainsString("\$conf['l1']['l2']['l3']['l4'] = 'deep';", $result);
+    }
+
+    public function testMixedNumericAndStringKeys(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $config = ['conf' => ['items' => [0 => 'zero', 'name' => 'value', 1 => 'one']]];
+        $result = $formatter->format($config);
+
+        // Numeric keys come first when sorted (0, 1, then 'name')
+        $this->assertStringContainsString("\$conf['items'][0] = 'zero';", $result);
+        $this->assertStringContainsString("\$conf['items'][1] = 'one';", $result);
+        $this->assertStringContainsString("\$conf['items']['name'] = 'value';", $result);
+    }
+
+    public function testRealWorldHordeConfig(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $config = [
+            'conf' => [
+                'sql' => [
+                    'hostspec' => 'localhost',
+                    'username' => 'horde',
+                    'password' => 'secret',
+                    'port' => 3306,
+                ],
+                'readwritesplit' => true,
+                'log_level' => new LiteralCode('Horde_Log::DEBUG'),
+            ],
+        ];
+
+        $result = $formatter->format($config);
+
+        $this->assertStringContainsString("\$conf['log_level'] = Horde_Log::DEBUG;", $result);
+        $this->assertStringContainsString("\$conf['readwritesplit'] = true;", $result);
+        $this->assertStringContainsString("\$conf['sql']['hostspec'] = 'localhost';", $result);
+        $this->assertStringContainsString("\$conf['sql']['password'] = 'secret';", $result);
+        $this->assertStringContainsString("\$conf['sql']['port'] = 3306;", $result);
+        $this->assertStringContainsString("\$conf['sql']['username'] = 'horde';", $result);
+    }
+
+    public function testEmptyStringValue(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['empty' => '']]);
+        $this->assertStringContainsString("\$conf['empty'] = '';", $result);
+    }
+
+    public function testZeroIntegerValue(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['zero' => 0]]);
+        $this->assertStringContainsString("\$conf['zero'] = 0;", $result);
+    }
+
+    public function testZeroFloatValue(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['zero' => 0.0]]);
+        $this->assertStringContainsString("\$conf['zero'] = 0;", $result);
+    }
+
+    public function testNegativeNumbers(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['int' => -42, 'float' => -3.14]]);
+        $this->assertStringContainsString("\$conf['float'] = -3.14;", $result);
+        $this->assertStringContainsString("\$conf['int'] = -42;", $result);
+    }
+
+    public function testUnicodeInKeys(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key_with_émojis_🎉' => 'value']]);
+        $this->assertStringContainsString('key_with_émojis_🎉', $result);
+    }
+
+    public function testUnicodeInValues(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key' => 'Héllo Wörld 🌍']]);
+        $this->assertStringContainsString('Héllo Wörld 🌍', $result);
+    }
+
+    public function testDoubleQuotesInValue(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key' => 'value "quoted"']]);
+        // addslashes() escapes double quotes
+        $this->assertStringContainsString('value \"quoted\"', $result);
+    }
+
+    public function testNewlineInValue(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key' => "line1\nline2"]]);
+        // addslashes() does NOT escape newlines - they remain literal
+        $this->assertStringContainsString("line1\nline2", $result);
+    }
+
+    public function testTabInValue(): void
+    {
+        $formatter = new ClassicHordeFormatter();
+        $result = $formatter->format(['conf' => ['key' => "col1\tcol2"]]);
+        // addslashes() does NOT escape tabs - they remain literal
+        $this->assertStringContainsString("col1\tcol2", $result);
+    }
+}
diff --git a/test/unit/Formatter/ModernArrayFormatterTest.php b/test/unit/Formatter/ModernArrayFormatterTest.php
new file mode 100644
index 0000000..56effea
--- /dev/null
+++ b/test/unit/Formatter/ModernArrayFormatterTest.php
@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Horde\PhpConfigFile\Test\Unit\Formatter;
+
+use Horde\PhpConfigFile\Formatter\ModernArrayFormatter;
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+#[CoversClass(ModernArrayFormatter::class)]
+class ModernArrayFormatterTest extends TestCase
+{
+    public function testFormatSimpleArray(): void
+    {
+        $formatter = new ModernArrayFormatter();
+        $result = $formatter->format(['key' => 'value']);
+        $this->assertStringContainsString("\$key = 'value';", $result);
+    }
+
+    public function testFormatNestedArray(): void
+    {
+        $formatter = new ModernArrayFormatter();
+        $config = ['outer' => ['inner' => 'value']];
+        $result = $formatter->format($config);
+        $this->assertStringContainsString("'inner' => 'value'", $result);
+        $this->assertStringContainsString('$outer = ', $result);
+    }
+
+    public function testFormatMultipleKeys(): void
+    {
+        $formatter = new ModernArrayFormatter();
+        $config = ['key1' => 'value1', 'key2' => 'value2'];
+        $result = $formatter->format($config);
+        $this->assertStringContainsString("\$key1 = 'value1';", $result);
+        $this->assertStringContainsString("\$key2 = 'value2';", $result);
+    }
+
+    public function testFormatArrayWithVarExport(): void
+    {
+        $formatter = new ModernArrayFormatter();
+        $config = ['config' => ['key' => 'value', 'num' => 42]];
+        $result = $formatter->format($config);
+        $this->assertStringContainsString('array (', $result);
+        $this->assertStringContainsString("'key' => 'value'", $result);
+    }
+
+    public function testFormatPreservesScalarBehavior(): void
+    {
+        $formatter = new ModernArrayFormatter();
+        $result = $formatter->format(['simple' => 'test']);
+        $this->assertEquals("\$simple = 'test';\n", $result);
+    }
+}
diff --git a/test/unit/Integration/FormatterIntegrationTest.php b/test/unit/Integration/FormatterIntegrationTest.php
new file mode 100644
index 0000000..0db11f1
--- /dev/null
+++ b/test/unit/Integration/FormatterIntegrationTest.php
@@ -0,0 +1,263 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Horde\PhpConfigFile\Test\Unit\Integration;
+
+use Horde\PhpConfigFile\PhpConfigFile;
+use Horde\PhpConfigFile\LiteralCode;
+use Horde\PhpConfigFile\Formatter\ClassicHordeFormatter;
+use Horde\PhpConfigFile\Formatter\ModernArrayFormatter;
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\Attributes\CoversNothing;
+
+use function file_get_contents;
+use function unlink;
+use function sys_get_temp_dir;
+use function uniqid;
+
+#[CoversNothing]
+class FormatterIntegrationTest extends TestCase
+{
+    private function getTempFile(): string
+    {
+        return sys_get_temp_dir() . '/phpconfigfile_test_' . uniqid() . '.php';
+    }
+
+    public function testWriteWithDefaultFormatterUsesModernFormat(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile($path);
+        $file->writeConfigFile(['config' => ['key' => 'value']]);
+
+        $content = file_get_contents($path);
+        $this->assertStringContainsString("'key' => 'value'", $content);
+        $this->assertStringNotContainsString("\$config['key']", $content);
+        unlink($path);
+    }
+
+    public function testWriteWithConstructorFormatterUsesClassicFormat(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile(
+            $path,
+            formatter: new ClassicHordeFormatter()
+        );
+        $file->writeConfigFile(['conf' => ['key' => 'value']]);
+
+        $content = file_get_contents($path);
+        $this->assertStringContainsString("\$conf['key'] = 'value';", $content);
+        unlink($path);
+    }
+
+    public function testWriteWithMethodFormatterOverridesConstructor(): void
+    {
+        $path = $this->getTempFile();
+        // Constructor has modern formatter
+        $file = new PhpConfigFile(
+            $path,
+            formatter: new ModernArrayFormatter()
+        );
+        // Method call overrides with classic formatter
+        $file->writeConfigFile(
+            ['conf' => ['key' => 'value']],
+            new ClassicHordeFormatter()
+        );
+
+        $content = file_get_contents($path);
+        $this->assertStringContainsString("\$conf['key'] = 'value';", $content);
+        $this->assertStringNotContainsString("'key' => 'value'", $content);
+        unlink($path);
+    }
+
+    public function testRoundTripClassicFormat(): void
+    {
+        $path = $this->getTempFile();
+        $formatter = new ClassicHordeFormatter();
+        $file = new PhpConfigFile($path, formatter: $formatter);
+
+        $original = [
+            'conf' => [
+                'sql' => [
+                    'host' => 'localhost',
+                    'port' => 3306,
+                ],
+                'enabled' => true,
+            ],
+        ];
+
+        $file->writeConfigFile($original);
+        $file->readConfigFile();
+        $parsed = $file->parseContent();
+
+        $this->assertEquals('localhost', $parsed['conf']['sql']['host']);
+        $this->assertEquals(3306, $parsed['conf']['sql']['port']);
+        $this->assertTrue($parsed['conf']['enabled']);
+
+        unlink($path);
+    }
+
+    public function testRoundTripModernFormat(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile($path);
+
+        $original = [
+            'config' => [
+                'key1' => 'value1',
+                'key2' => 'value2',
+            ],
+        ];
+
+        $file->writeConfigFile($original);
+        $file->readConfigFile();
+        $parsed = $file->parseContent();
+
+        $this->assertEquals('value1', $parsed['config']['key1']);
+        $this->assertEquals('value2', $parsed['config']['key2']);
+
+        unlink($path);
+    }
+
+    public function testRoundTripWithLiteralCode(): void
+    {
+        $path = $this->getTempFile();
+        $formatter = new ClassicHordeFormatter();
+        $file = new PhpConfigFile($path, formatter: $formatter);
+
+        // Define constant for test
+        if (!defined('TEST_CONSTANT')) {
+            define('TEST_CONSTANT', 42);
+        }
+
+        $original = [
+            'conf' => [
+                'value' => new LiteralCode('TEST_CONSTANT'),
+            ],
+        ];
+
+        $file->writeConfigFile($original);
+        $file->readConfigFile();
+        $parsed = $file->parseContent();
+
+        $this->assertEquals(42, $parsed['conf']['value']);
+
+        unlink($path);
+    }
+
+    public function testPreservesContentBeforeHeader(): void
+    {
+        $path = $this->getTempFile();
+
+        // Write initial content with pre-header section
+        file_put_contents($path, "<?php\n// Pre-header comment\n\$prevar = 'preserved';\n/* BEGIN */\n\$old = 'data';\n/* END */\n");
+
+        $file = new PhpConfigFile(
+            $path,
+            header: '/* BEGIN */',
+            footer: '/* END */',
+            formatter: new ClassicHordeFormatter()
+        );
+
+        $file->readConfigFile();
+        $file->writeConfigFile(['conf' => ['key' => 'value']]);
+
+        $content = file_get_contents($path);
+        $this->assertStringContainsString('// Pre-header comment', $content);
+        $this->assertStringContainsString("\$prevar = 'preserved';", $content);
+        $this->assertStringContainsString("\$conf['key'] = 'value';", $content);
+
+        unlink($path);
+    }
+
+    public function testPreservesContentAfterFooter(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile(
+            $path,
+            header: '/* BEGIN */',
+            footer: '/* END */',
+            formatter: new ClassicHordeFormatter()
+        );
+
+        // Write initial content with footer content
+        file_put_contents(
+            $path,
+            "<?php\n/* BEGIN */\n/* END */\n// Post-footer comment\n\$postvar = 'preserved';\n"
+        );
+
+        $file->readConfigFile();
+        $file->writeConfigFile(['conf' => ['key' => 'value']]);
+
+        $content = file_get_contents($path);
+        $this->assertStringContainsString('// Post-footer comment', $content);
+        $this->assertStringContainsString("\$postvar = 'preserved';", $content);
+        $this->assertStringContainsString("\$conf['key'] = 'value';", $content);
+
+        unlink($path);
+    }
+
+    public function testAlphabeticalOrderingInOutput(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile($path, formatter: new ClassicHordeFormatter());
+
+        $config = [
+            'conf' => [
+                'z_last' => 'last',
+                'a_first' => 'first',
+                'm_middle' => 'middle',
+            ],
+        ];
+
+        $file->writeConfigFile($config);
+        $content = file_get_contents($path);
+
+        // Verify alphabetical order
+        $posA = strpos($content, "\$conf['a_first']");
+        $posM = strpos($content, "\$conf['m_middle']");
+        $posZ = strpos($content, "\$conf['z_last']");
+
+        $this->assertLessThan($posM, $posA);
+        $this->assertLessThan($posZ, $posM);
+
+        unlink($path);
+    }
+
+    public function testMultipleWritesWithSameFormatter(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile($path, formatter: new ClassicHordeFormatter());
+
+        $file->writeConfigFile(['conf' => ['key1' => 'value1']]);
+        $content1 = file_get_contents($path);
+        $this->assertStringContainsString("\$conf['key1'] = 'value1';", $content1);
+
+        // Second write with different data
+        $file->writeConfigFile(['conf' => ['key2' => 'value2']]);
+        $content2 = file_get_contents($path);
+        $this->assertStringContainsString("\$conf['key2'] = 'value2';", $content2);
+        $this->assertStringNotContainsString('key1', $content2);
+
+        unlink($path);
+    }
+
+    public function testSwitchFormatterBetweenWrites(): void
+    {
+        $path = $this->getTempFile();
+        $file = new PhpConfigFile($path);
+
+        // Write with classic format
+        $file->writeConfigFile(['conf' => ['key' => 'value']], new ClassicHordeFormatter());
+        $content1 = file_get_contents($path);
+        $this->assertStringContainsString("\$conf['key'] = 'value';", $content1);
+
+        // Write with modern format
+        $file->writeConfigFile(['config' => ['key' => 'value']], new ModernArrayFormatter());
+        $content2 = file_get_contents($path);
+        $this->assertStringContainsString("'key' => 'value'", $content2);
+        $this->assertStringNotContainsString("\$config['key']", $content2);
+
+        unlink($path);
+    }
+}
diff --git a/test/unit/LiteralCodeTest.php b/test/unit/LiteralCodeTest.php
new file mode 100644
index 0000000..a4b5d7a
--- /dev/null
+++ b/test/unit/LiteralCodeTest.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Horde\PhpConfigFile\Test\Unit;
+
+use Horde\PhpConfigFile\LiteralCode;
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+#[CoversClass(LiteralCode::class)]
+class LiteralCodeTest extends TestCase
+{
+    public function testConstructorStoresCode(): void
+    {
+        $literal = new LiteralCode('SomeClass::CONSTANT');
+        $this->assertEquals('SomeClass::CONSTANT', $literal->getCode());
+    }
+
+    public function testToStringReturnsCode(): void
+    {
+        $literal = new LiteralCode('60 * 60');
+        $this->assertEquals('60 * 60', (string) $literal);
+    }
+
+    public function testSupportsExpression(): void
+    {
+        $literal = new LiteralCode('Horde_Log::DEBUG');
+        $this->assertEquals('Horde_Log::DEBUG', $literal->getCode());
+    }
+
+    public function testSupportsComplexExpression(): void
+    {
+        $literal = new LiteralCode('defined("DEBUG") ? 1 : 0');
+        $this->assertEquals('defined("DEBUG") ? 1 : 0', $literal->getCode());
+    }
+
+    public function testIsReadonly(): void
+    {
+        $literal = new LiteralCode('test');
+        $reflection = new \ReflectionClass($literal);
+        $this->assertTrue($reflection->isReadOnly());
+    }
+}
diff --git a/test/unit/PhpConfigFileTest.php b/test/unit/PhpConfigFileTest.php
index 827c313..ba5d1e8 100644
--- a/test/unit/PhpConfigFileTest.php
+++ b/test/unit/PhpConfigFileTest.php
@@ -7,8 +7,9 @@
 use Horde\PhpConfigFile\PhpConfigFile;
 use PHPUnit\Framework\TestCase;
 use Stringable;
-use PHPUnit\Framework\Attributes\CoversNothing;
-#[CoversNothing]
+use PHPUnit\Framework\Attributes\CoversClass;
+
+#[CoversClass(PhpConfigFile::class)]
 class PhpConfigFileTest extends TestCase
 {
     public function testReadEmptyConfigFile(): void
@@ -112,4 +113,43 @@ public function testReadFailure(): void
         );
         $file->readConfigFile();
     }
+
+    public function testParseContentWithInvalidArea(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid area to parse from');
+
+        $file = new PhpConfigFile(
+            configFilePath: __DIR__ . '/../fixtures/EmptyConfigFile.php',
+        );
+        $file->readConfigFile();
+        $file->parseContent('invalid_area');
+    }
+
+    public function testWriteWithDefaultFormatter(): void
+    {
+        $file = new PhpConfigFile('deleteme_default');
+        $file->writeConfigFile(['key' => 'value']);
+
+        $this->assertFileExists('deleteme_default');
+        $content = (string) file_get_contents('deleteme_default');
+        // Should use ModernArrayFormatter by default
+        $this->assertStringContainsString("\$key = 'value';", $content);
+        unlink('deleteme_default');
+    }
+
+    public function testGettersReturnCorrectContent(): void
+    {
+        $file = new PhpConfigFile(
+            configFilePath: __DIR__ . '/../fixtures/WithPreHeaderAndPostFooterContent.php',
+            header: '/* Begin Horde Config File - do not edit */',
+            footer: '/* End Horde Config File - do not edit */'
+        );
+        $file->readConfigFile();
+
+        $this->assertNotEmpty($file->getContent());
+        $this->assertNotEmpty($file->getContentBeforeHeader());
+        $this->assertNotEmpty($file->getContentAfterFooter());
+        $this->assertNotEmpty($file->getContentBetweenHeaderAndFooter());
+    }
 }