diff --git a/src/CommandLine/Parser.php b/src/CommandLine/Parser.php
index 10ee384..0c75125 100644
--- a/src/CommandLine/Parser.php
+++ b/src/CommandLine/Parser.php
@@ -16,12 +16,31 @@
 class Parser
 {
 	public const
-		ARGUMENT = 'argument',
-		OPTIONAL = 'optional',
-		REPEATABLE = 'repeatable',
-		ENUM = 'enum',
-		REALPATH = 'realpath',
-		VALUE = 'default';
+		Argument = 'argument',
+		Optional = 'optional',
+		Repeatable = 'repeatable',
+		Enum = 'enum',
+		RealPath = 'realpath',
+		Default = 'default';
+
+	/** @deprecated use Parser::Argument */
+	public const ARGUMENT = self::Argument;
+
+	/** @deprecated use Parser::Optional */
+	public const OPTIONAL = self::Optional;
+
+	/** @deprecated use Parser::Repeatable */
+	public const REPEATABLE = self::Repeatable;
+
+	/** @deprecated use Parser::Enum */
+	public const ENUM = self::Enum;
+
+	/** @deprecated use Parser::Realpath */
+	public const REALPATH = self::RealPath;
+
+	/** @deprecated use Parser::Default */
+	public const VALUE = self::Default;
+
 
 	/** @var array[] */
 	private $options = [];
@@ -51,11 +70,11 @@ public function __construct(string $help, array $defaults = [])
 			$name = end($m[1]);
 			$opts = $this->options[$name] ?? [];
 			$this->options[$name] = $opts + [
-				self::ARGUMENT => (bool) end($m[2]),
-				self::OPTIONAL => isset($line[2]) || (substr(end($m[2]), 0, 1) === '[') || isset($opts[self::VALUE]),
-				self::REPEATABLE => (bool) end($m[3]),
-				self::ENUM => count($enums = explode('|', trim(end($m[2]), '<[]>'))) > 1 ? $enums : null,
-				self::VALUE => $line[2] ?? null,
+				self::Argument => (bool) end($m[2]),
+				self::Optional => isset($line[2]) || (substr(end($m[2]), 0, 1) === '[') || isset($opts[self::Default]),
+				self::Repeatable => (bool) end($m[3]),
+				self::Enum => count($enums = explode('|', trim(end($m[2]), '<[]>'))) > 1 ? $enums : null,
+				self::Default => $line[2] ?? null,
 			];
 			if ($name !== $m[1][0]) {
 				$this->aliases[$m[1][0]] = $name;
@@ -88,7 +107,7 @@ public function parse(?array $args = null): array
 
 				$name = current($this->positional);
 				$this->checkArg($this->options[$name], $arg);
-				if (empty($this->options[$name][self::REPEATABLE])) {
+				if (empty($this->options[$name][self::Repeatable])) {
 					$params[$name] = $arg;
 					next($this->positional);
 				} else {
@@ -109,31 +128,31 @@ public function parse(?array $args = null): array
 
 			$opt = $this->options[$name];
 
-			if ($arg !== true && empty($opt[self::ARGUMENT])) {
+			if ($arg !== true && empty($opt[self::Argument])) {
 				throw new \Exception("Option $name has not argument.");
 
-			} elseif ($arg === true && !empty($opt[self::ARGUMENT])) {
+			} elseif ($arg === true && !empty($opt[self::Argument])) {
 				if (isset($args[$i]) && $args[$i][0] !== '-') {
 					$arg = $args[$i++];
-				} elseif (empty($opt[self::OPTIONAL])) {
+				} elseif (empty($opt[self::Optional])) {
 					throw new \Exception("Option $name requires argument.");
 				}
 			}
 
 			if (
-				!empty($opt[self::ENUM])
-				&& !in_array($arg, $opt[self::ENUM], true)
+				!empty($opt[self::Enum])
+				&& !in_array($arg, $opt[self::Enum], true)
 				&& !(
-					$opt[self::OPTIONAL]
+					$opt[self::Optional]
 					&& $arg === true
 				)
 			) {
-				throw new \Exception("Value of option $name must be " . implode(', or ', $opt[self::ENUM]) . '.');
+				throw new \Exception("Value of option $name must be " . implode(', or ', $opt[self::Enum]) . '.');
 			}
 
 			$this->checkArg($opt, $arg);
 
-			if (empty($opt[self::REPEATABLE])) {
+			if (empty($opt[self::Repeatable])) {
 				$params[$name] = $arg;
 			} else {
 				$params[$name][] = $arg;
@@ -143,15 +162,15 @@ public function parse(?array $args = null): array
 		foreach ($this->options as $name => $opt) {
 			if (isset($params[$name])) {
 				continue;
-			} elseif (isset($opt[self::VALUE])) {
-				$params[$name] = $opt[self::VALUE];
-			} elseif ($name[0] !== '-' && empty($opt[self::OPTIONAL])) {
+			} elseif (isset($opt[self::Default])) {
+				$params[$name] = $opt[self::Default];
+			} elseif ($name[0] !== '-' && empty($opt[self::Optional])) {
 				throw new \Exception("Missing required argument <$name>.");
 			} else {
 				$params[$name] = null;
 			}
 
-			if (!empty($opt[self::REPEATABLE])) {
+			if (!empty($opt[self::Repeatable])) {
 				$params[$name] = (array) $params[$name];
 			}
 		}
@@ -168,7 +187,7 @@ public function help(): void
 
 	public function checkArg(array $opt, &$arg): void
 	{
-		if (!empty($opt[self::REALPATH])) {
+		if (!empty($opt[self::RealPath])) {
 			$path = realpath($arg);
 			if ($path === false) {
 				throw new \Exception("File path '$arg' not found.");
diff --git a/tests/Parser.phpt b/tests/Parser.phpt
index c38cc3a..4031106 100644
--- a/tests/Parser.phpt
+++ b/tests/Parser.phpt
@@ -40,7 +40,7 @@ test('default value', function () {
 	$cmd = new Parser('
 		-p
 	', [
-		'-p' => [Parser::VALUE => 123],
+		'-p' => [Parser::Default => 123],
 	]);
 
 	Assert::same(['-p' => 123], $cmd->parse([]));
@@ -116,7 +116,7 @@ test('optional argument', function () {
 	$cmd = new Parser('
 		-p param
 	', [
-		'-p' => [Parser::VALUE => 123],
+		'-p' => [Parser::Default => 123],
 	]);
 
 	Assert::same(['-p' => 123], $cmd->parse([]));
@@ -127,7 +127,7 @@ test('optional argument', function () {
 	$cmd = new Parser('
 		-p param
 	', [
-		'-p' => [Parser::OPTIONAL => true],
+		'-p' => [Parser::Optional => true],
 	]);
 
 	Assert::same(['-p' => null], $cmd->parse([]));
@@ -183,7 +183,7 @@ test('realpath', function () {
 	$cmd = new Parser('
 		-p <path>
 	', [
-		'-p' => [Parser::REALPATH => true],
+		'-p' => [Parser::RealPath => true],
 	]);
 
 	Assert::exception(function () use ($cmd) {
@@ -210,21 +210,21 @@ test('positional arguments', function () {
 	}, Throwable::class, 'Unexpected parameter val2.');
 
 	$cmd = new Parser('', [
-		'pos' => [Parser::REPEATABLE => true],
+		'pos' => [Parser::Repeatable => true],
 	]);
 
 	Assert::same(['pos' => ['val1', 'val2']], $cmd->parse(['val1', 'val2']));
 
 
 	$cmd = new Parser('', [
-		'pos' => [Parser::OPTIONAL => true],
+		'pos' => [Parser::Optional => true],
 	]);
 
 	Assert::same(['pos' => null], $cmd->parse([]));
 
 
 	$cmd = new Parser('', [
-		'pos' => [Parser::VALUE => 'default', Parser::REPEATABLE => true],
+		'pos' => [Parser::Default => 'default', Parser::Repeatable => true],
 	]);
 
 	Assert::same(['pos' => ['default']], $cmd->parse([]));