diff --git a/src/Bytes.php b/src/Bytes.php
index 33141bc..6437349 100644
--- a/src/Bytes.php
+++ b/src/Bytes.php
@@ -4,7 +4,7 @@
 
 namespace gapple\StructuredFields;
 
-class Bytes
+class Bytes implements \Stringable
 {
     public function __construct(private readonly string $value)
     {
diff --git a/src/Dictionary.php b/src/Dictionary.php
index c07259b..4c2fd55 100644
--- a/src/Dictionary.php
+++ b/src/Dictionary.php
@@ -37,7 +37,6 @@ public static function fromArray(array $array): self
     }
 
     /**
-     * @param string $name
      * @return TupleInterface|array{mixed, object}|null
      */
     public function __get(string $name): mixed
@@ -46,9 +45,7 @@ public function __get(string $name): mixed
     }
 
     /**
-     * @param string $name
      * @param TupleInterface|array{mixed, object} $value
-     * @return void
      */
     public function __set(string $name, mixed $value): void
     {
diff --git a/src/DisplayString.php b/src/DisplayString.php
index ecc6cb0..ef9aca2 100644
--- a/src/DisplayString.php
+++ b/src/DisplayString.php
@@ -4,7 +4,7 @@
 
 namespace gapple\StructuredFields;
 
-class DisplayString
+class DisplayString implements \Stringable
 {
     public function __construct(private readonly string $value)
     {
diff --git a/src/InnerList.php b/src/InnerList.php
index 88cbca3..11a3160 100644
--- a/src/InnerList.php
+++ b/src/InnerList.php
@@ -10,7 +10,6 @@ class InnerList implements TupleInterface
 
     /**
      * @param array<TupleInterface|array{mixed, object}> $value
-     * @param object|null $parameters
      */
     public function __construct(array $value, ?object $parameters = null)
     {
@@ -25,11 +24,10 @@ public function __construct(array $value, ?object $parameters = null)
      *
      * @param array<mixed> $array
      *   An array of bare items or TupleInterface objects.
-     * @return InnerList
      */
     public static function fromArray(array $array): InnerList
     {
-        array_walk($array, function (&$item) {
+        array_walk($array, function (&$item): void {
             if (!$item instanceof TupleInterface) {
                 $item = new Item($item);
             } elseif ($item instanceof InnerList) {
@@ -43,7 +41,6 @@ public static function fromArray(array $array): InnerList
 
     /**
      * @param TupleInterface|array{mixed, object} $value
-     * @return void
      */
     private static function validateItemType(mixed $value): void
     {
diff --git a/src/Item.php b/src/Item.php
index a89cda9..6f11f7a 100644
--- a/src/Item.php
+++ b/src/Item.php
@@ -8,10 +8,6 @@ class Item implements TupleInterface
 {
     use TupleTrait;
 
-    /**
-     * @param mixed $value
-     * @param object|null $parameters
-     */
     public function __construct(mixed $value, ?object $parameters = null)
     {
         $this->value = $value;
diff --git a/src/OuterList.php b/src/OuterList.php
index ea3bcfd..05708c6 100644
--- a/src/OuterList.php
+++ b/src/OuterList.php
@@ -31,11 +31,10 @@ public function __construct(array $value = [])
      * Create an OuterList from an array of bare values.
      *
      * @param array<mixed> $array
-     * @return OuterList
      */
     public static function fromArray(array $array): OuterList
     {
-        array_walk($array, function (&$item) {
+        array_walk($array, function (&$item): void {
             if (!$item instanceof TupleInterface) {
                 if (is_array($item)) {
                     $item = InnerList::fromArray($item);
@@ -51,7 +50,6 @@ public static function fromArray(array $array): OuterList
 
     /**
      * @param TupleInterface|array{mixed, object} $value
-     * @return void
      */
     private static function validateItemType(mixed $value): void
     {
@@ -77,7 +75,6 @@ public function getIterator(): \Iterator
 
     /**
      * @param int $offset
-     * @return bool
      */
     public function offsetExists($offset): bool
     {
@@ -86,7 +83,6 @@ public function offsetExists($offset): bool
 
     /**
      * @param int $offset
-     * @return mixed
      * @phpstan-return TupleInterface|array{mixed, object}|null
      */
     public function offsetGet($offset): mixed
@@ -97,7 +93,6 @@ public function offsetGet($offset): mixed
     /**
      * @param int|null $offset
      * @param TupleInterface|array{mixed, object} $value
-     * @return void
      */
     public function offsetSet($offset, $value): void
     {
@@ -112,7 +107,6 @@ public function offsetSet($offset, $value): void
 
     /**
      * @param int $offset
-     * @return void
      */
     public function offsetUnset($offset): void
     {
diff --git a/src/Parameters.php b/src/Parameters.php
index 63aefb7..8d0f76b 100644
--- a/src/Parameters.php
+++ b/src/Parameters.php
@@ -26,20 +26,11 @@ public static function fromArray(array $array): self
         return $parameters;
     }
 
-    /**
-     * @param string $name
-     * @return mixed|null
-     */
     public function __get(string $name): mixed
     {
         return $this->value[$name] ?? null;
     }
 
-    /**
-     * @param string $name
-     * @param mixed $value
-     * @return void
-     */
     public function __set(string $name, mixed $value): void
     {
         $this->value[$name] = $value;
diff --git a/src/Parser.php b/src/Parser.php
index f173274..8574963 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -20,8 +20,7 @@ public static function parseDictionary(string $string): Dictionary
         while (true) {
             $key = self::parseKey($input);
 
-            if ($input->isChar('=')) {
-                $input->consumeChar();
+            if ($input->skipNextCharIf('=')) {
                 $value->{$key} = self::parseItemOrInnerList($input);
             } else {
                 // Bare boolean true value.
@@ -85,7 +84,7 @@ public static function parseList(string $string): OuterList
 
     private static function parseItemOrInnerList(ParsingInput $input): TupleInterface
     {
-        if ($input->isChar('(')) {
+        if ($input->isNextChar('(')) {
             return self::parseInnerList($input);
         } else {
             return self::doParseItem($input);
@@ -104,8 +103,7 @@ private static function parseInnerList(ParsingInput $input): InnerList
         while (!$input->empty()) {
             $input->trim();
 
-            if ($input->isChar(')')) {
-                $input->consumeChar();
+            if ($input->skipNextCharIf(')')) {
                 return new InnerList(
                     $value,
                     self::parseParameters($input)
@@ -114,7 +112,7 @@ private static function parseInnerList(ParsingInput $input): InnerList
 
             $value[] = self::doParseItem($input);
 
-            if (!($input->isChar(' ') || $input->isChar(')'))) {
+            if (!($input->isNextChar(' ') || $input->isNextChar(')'))) {
                 if ($input->empty()) {
                     break;
                 }
@@ -126,8 +124,6 @@ private static function parseInnerList(ParsingInput $input): InnerList
     }
 
     /**
-     * @param string $string
-     *
      * @return Item
      *  A [value, parameters] tuple.
      */
@@ -190,16 +186,15 @@ private static function parseBareItem(ParsingInput $input): mixed
     private static function parseParameters(ParsingInput $input): Parameters
     {
         $parameters = new Parameters();
-        while ($input->isChar(';')) {
-            $input->consumeChar();
+        while ($input->skipNextCharIf(';')) {
             $input->trim();
 
             $key = self::parseKey($input);
-            $parameters->{$key} = true;
 
-            if ($input->isChar('=')) {
-                $input->consumeChar();
+            if ($input->skipNextCharIf('=')) {
                 $parameters->{$key} = self::parseBareItem($input);
+            } else {
+                $parameters->{$key} = true;
             }
         }
 
@@ -275,7 +270,7 @@ private static function parseString(ParsingInput $input): string
                 }
             } elseif ($char === '"') {
                 return $output;
-            } elseif (ord($char) <= 0x1f || ord($char) >= 0x7f) {
+            } elseif (!ctype_print($char)) {
                 throw new ParseException('Invalid character in string at position ' . ($input->position() - 1));
             }
 
@@ -301,18 +296,21 @@ private static function parseDisplayString(ParsingInput $string): DisplayString
         while (!$string->empty()) {
             $char = $string->consumeChar();
 
-            if (ord($char) <= 0x1f || ord($char) >= 0x7f) {
+            if (!ctype_print($char)) {
                 throw new ParseException(
                     'Invalid character in display string at position ' . ($string->position() - 1)
                 );
             } elseif ($char === '%') {
-                try {
-                    $encodedString .= '%' . $string->consumeRegex('/^[0-9a-f]{2}/');
-                } catch (\RuntimeException) {
+                if ($string->remainingLength() < 2) {
+                    break;
+                }
+                $encodedChar = $string->consume(2);
+                if (!ctype_xdigit($encodedChar) || ctype_upper($encodedChar)) {
                     throw new ParseException(
                         'Invalid hex values in display string at position ' . ($string->position() - 1)
                     );
                 }
+                $encodedString .= '%' . $encodedChar;
             } elseif ($char === '"') {
                 $displayString = new DisplayString(rawurldecode($encodedString));
                 // An invalid UTF-8 subject will cause the preg_* function to match nothing.
@@ -334,16 +332,19 @@ private static function parseDisplayString(ParsingInput $string): DisplayString
      */
     private static function parseToken(ParsingInput $input): Token
     {
-        // Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
-        // 3.2.6. Field Value Components
-        // @see https://tools.ietf.org/html/rfc7230#section-3.2.6
-        $tchar = preg_quote("!#$%&'*+-.^_`|~");
+        // RFC 9110: HTTP Semantics (5.6.2. Tokens)
+        // @see https://www.rfc-editor.org/rfc/rfc9110.html#name-tokens
+        // $tchar = preg_quote("!#$%&'*+-.^_`|~");
+        $tchar = "!#$%&'*+\-.^_`|~";
 
         // parseToken is only called by parseBareItem if the initial character
         // is valid, so a Token object is always returned.  If there is an
         // invalid character in the token, the public function that was called
         // will detect that the remainder of the input string is invalid.
-        return new Token($input->consumeRegex('/^([a-z*][a-z0-9:\/' . $tchar . ']*)/i'));
+        return new Token($input->consumeRegex('/^(
+                (?:\*|[a-z])                # an alphabetic character or "*"
+                [a-z0-9:\/' . $tchar . ']*  # zero to many token characters
+            )/ix'));
     }
 
     /**
diff --git a/src/ParsingInput.php b/src/ParsingInput.php
index 89bb1a2..fa09a0b 100644
--- a/src/ParsingInput.php
+++ b/src/ParsingInput.php
@@ -33,13 +33,17 @@ public function remaining(): string
         return substr($this->value, $this->position);
     }
 
+    public function remainingLength(): int
+    {
+        return $this->length - $this->position();
+    }
+
     /**
      * Trim whitespace from beginning of string.
      *
      * @param bool $ows
      *   Whether all Optional Whitespace characters should be trimmed.  If false, only space characters are trimmed.
      *   @see https://tools.ietf.org/html/rfc7230#section-3.2.3
-     * @return void
      */
     public function trim(bool $ows = false): void
     {
@@ -54,7 +58,16 @@ public function trim(bool $ows = false): void
         }
     }
 
+    /**
+     * @deprecated in 2.3.0 and will be removed in 3.0.0
+     * @codeCoverageIgnore
+     */
     public function isChar(string $char): bool
+    {
+        return $this->isNextChar($char);
+    }
+
+    public function isNextChar(string $char): bool
     {
         assert(strlen($char) === 1);
 
@@ -70,6 +83,15 @@ public function getChar(): string
         return $this->value[$this->position];
     }
 
+    public function skipNextCharIf(string $char): bool
+    {
+        if ($this->isNextChar($char)) {
+            $this->position++;
+            return true;
+        }
+        return false;
+    }
+
     /**
      * @phpstan-impure
      */
@@ -114,6 +136,7 @@ public function consumeString(string $value): void
     public function consumeRegex(string $pattern): string
     {
         assert(str_starts_with($pattern, '/^'));
+        assert(!preg_match('/\$\/[a-z]+$/i', $pattern));
 
         if (preg_match($pattern, $this->remaining(), $matches)) {
             $this->position += strlen($matches[0]);
diff --git a/src/Serializer.php b/src/Serializer.php
index d86c4df..f5874fd 100644
--- a/src/Serializer.php
+++ b/src/Serializer.php
@@ -9,13 +9,10 @@ class Serializer
     /**
      * Serialize an item with optional parameters.
      *
-     * @param mixed $value
+     * @param Item|mixed $value
      *   A bare value, or an Item object.
      * @param object|null $parameters
-     *   An optional object containing parameter values if a bare value is provided.
-     *
-     * @return string
-     *   The serialized value.
+     *   If a bare value is provided, an optional object containing parameter values.
      */
     public static function serializeItem(mixed $value, ?object $parameters = null): string
     {
@@ -43,7 +40,6 @@ public static function serializeItem(mixed $value, ?object $parameters = null):
 
     /**
      * @param iterable<TupleInterface|array{mixed, object}> $value
-     * @return string
      */
     public static function serializeList(iterable $value): string
     {
@@ -205,11 +201,10 @@ private static function serializeDecimal(float $value): string
 
     private static function serializeString(string $value): string
     {
-        if (preg_match('/[^\x20-\x7E]/i', $value)) {
+        if (!empty($value) && !ctype_print($value)) {
             throw new SerializeException("Invalid characters in string");
         }
-
-        return '"' . preg_replace('/(["\\\])/', '\\\$1', $value) . '"';
+        return '"' . str_replace(['\\', '"'], ['\\\\', '\"'], $value) . '"';
     }
 
     private static function serializeDisplayString(DisplayString $value): string
@@ -224,12 +219,17 @@ private static function serializeDisplayString(DisplayString $value): string
 
     private static function serializeToken(Token $value): string
     {
-        // Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
-        // 3.2.6. Field Value Components
-        // @see https://tools.ietf.org/html/rfc7230#section-3.2.6
-        $tchar = preg_quote("!#$%&'*+-.^_`|~");
-
-        if (!preg_match('/^((?:\*|[a-z])[a-z0-9:\/' . $tchar . ']*)$/i', (string) $value)) {
+        // RFC 9110: HTTP Semantics (5.6.2. Tokens)
+        // @see https://www.rfc-editor.org/rfc/rfc9110.html#name-tokens
+        // $tchar = preg_quote("!#$%&'*+-.^_`|~");
+        $tchar = "!#$%&'*+\-.^_`|~";
+
+        if (
+            !preg_match('/^(
+                (?:\*|[a-z])                # an alphabetic character or "*"
+                [a-z0-9:\/' . $tchar . ']*  # zero to many token characters
+            )$/ix', (string) $value)
+        ) {
             throw new SerializeException('Invalid characters in token');
         }
 
diff --git a/src/Token.php b/src/Token.php
index 9083357..a8543ea 100644
--- a/src/Token.php
+++ b/src/Token.php
@@ -4,7 +4,7 @@
 
 namespace gapple\StructuredFields;
 
-class Token
+class Token implements \Stringable
 {
     public function __construct(private readonly string $value)
     {
diff --git a/src/TupleTrait.php b/src/TupleTrait.php
index 86c3329..5a9bdb6 100644
--- a/src/TupleTrait.php
+++ b/src/TupleTrait.php
@@ -39,7 +39,6 @@ public function offsetExists($offset): bool
 
     /**
      * @param 0|1 $offset
-     * @return mixed
      * @phpstan-return ($offset is 0 ? mixed : $offset is 1 ? object : null)
      */
     public function offsetGet($offset): mixed
diff --git a/tests/Httpwg/HttpwgRuleExpectedConverter.php b/tests/Httpwg/HttpwgRuleExpectedConverter.php
index 09a118d..13f4161 100644
--- a/tests/Httpwg/HttpwgRuleExpectedConverter.php
+++ b/tests/Httpwg/HttpwgRuleExpectedConverter.php
@@ -29,7 +29,6 @@ class HttpwgRuleExpectedConverter
      * Convert the expected value of an item tuple.
      *
      * @param  ExpectedItem $item
-     * @return Item
      */
     public static function item(array $item): Item
     {
@@ -40,7 +39,6 @@ public static function item(array $item): Item
      * Convert the expected values of a dictionary.
      *
      * @param  ExpectedDictionary $dictionary
-     * @return Dictionary
      */
     public static function dictionary(array $dictionary): Dictionary
     {
@@ -66,7 +64,6 @@ public static function dictionary(array $dictionary): Dictionary
      * Convert the expected values of a list.
      *
      * @param  ExpectedOuterList $list
-     * @return OuterList
      */
     public static function list(array $list): OuterList
     {
@@ -86,8 +83,7 @@ public static function list(array $list): OuterList
     /**
      * Convert the expected values of a parameters map.
      *
-     * @param  ExpectedParameters $parameters
-     * @return Parameters
+     * @param ExpectedParameters $parameters
      */
     private static function parameters(array $parameters): Parameters
     {
@@ -95,7 +91,7 @@ private static function parameters(array $parameters): Parameters
 
         foreach ($parameters as $value) {
             // Null byte is not supported as first character of property name.
-            if (strpos($value[0], "\0") === 0) {
+            if (str_starts_with($value[0], "\0")) {
                 throw new \UnexpectedValueException();
             }
 
@@ -109,7 +105,6 @@ private static function parameters(array $parameters): Parameters
      * Convert the expected values of an inner list tuple.
      *
      * @param  ExpectedInnerList $innerList
-     * @return InnerList
      */
     private static function innerList(array $innerList): InnerList
     {
diff --git a/tests/ParsingInputTest.php b/tests/ParsingInputTest.php
index fa347f9..221f4f8 100644
--- a/tests/ParsingInputTest.php
+++ b/tests/ParsingInputTest.php
@@ -4,6 +4,7 @@
 
 use gapple\StructuredFields\ParsingInput;
 use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\RequiresSetting;
 use PHPUnit\Framework\TestCase;
 
 class ParsingInputTest extends TestCase
@@ -21,6 +22,7 @@ public function testGetEmptyChar(): void
     public static function trimProvider(): array
     {
         return [
+            // [input string, trim optional white space, expected remaining string]
             'space' => ['  test ', false, 'test '],
             'ows' => [" \t test ", true, 'test '],
             'non-ows' => [" \t test ", false, "\t test "],
@@ -51,4 +53,37 @@ public function testConsumeNotMatched(): void
         $this->expectExceptionMessage('Unexpected character');
         $input->consumeString('foo');
     }
+
+    /**
+     * @return array<string, array{string, bool}>
+     */
+    public static function regexProvider(): array
+    {
+        return [
+            'Valid' => ['/^test/', true],
+            'Valid with modifier' => ['/^test/i', true],
+            'Missing start anchor' => ['/test/', false],
+            'End anchor' => ['/test$/', false],
+            'End anchor and modifier' => ['/test$/i', false],
+        ];
+    }
+
+    #[RequiresSetting('zend.assertions', '1')]
+    #[DataProvider('regexProvider')]
+    public function testConsumeRegex(string $regex, bool $expected): void
+    {
+        try {
+            $input = new ParsingInput('test');
+            $input->consumeRegex($regex);
+
+            if (!$expected) {
+                $this->fail('Expression should not have passed assertions');
+            }
+        } catch (\AssertionError $e) {
+            if ($expected) {
+                $this->fail('Expression failed assertion: ' . $e->getMessage());
+            }
+        }
+        $this->addToAssertionCount(1);
+    }
 }