diff --git a/system/core/Input.php b/system/core/Input.php
index a2fca18f613..90552e8ee6a 100644
--- a/system/core/Input.php
+++ b/system/core/Input.php
@@ -390,7 +390,7 @@ public function set_cookie($name, $value = '', $expire = 0, $domain = '', $path
 			'httponly' => $httponly,
 			'samesite' => $samesite,
 		);
-		setcookie($prefix.$name, (string) $value, $setcookie_options);
+		setcookie($prefix.$name, $value === NULL ? '' : $value, $setcookie_options);
 	}
 
 	// --------------------------------------------------------------------
diff --git a/system/core/Output.php b/system/core/Output.php
index 7a908bf25c3..7c4a759c2b3 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -558,8 +558,7 @@ public function _display($output = NULL)
 	public function _write_cache($output)
 	{
 		$CI =& get_instance();
-		$path = $CI->config->item('cache_path');
-		$cache_path = ($path === '') ? APPPATH.'cache'.DIRECTORY_SEPARATOR : rtrim($path, '/\\').DIRECTORY_SEPARATOR;
+		$cache_path = $this->_get_cache_path($CI->config->item('cache_path'));
 
 		if ( ! is_dir($cache_path) OR ! is_really_writable($cache_path))
 		{
@@ -660,8 +659,7 @@ public function _write_cache($output)
 	 */
 	public function _display_cache(&$CFG, &$URI)
 	{
-		$path = $CFG->item('cache_path');
-		$cache_path = ($path === '') ? APPPATH.'cache'.DIRECTORY_SEPARATOR : rtrim($path, '/\\').DIRECTORY_SEPARATOR;
+		$cache_path = $this->_get_cache_path($CFG->item('cache_path'));
 
 		// Build the file path. The file name is an MD5 hash of the full URI
 		$uri = $CFG->item('base_url').$CFG->slash_item('index_page').$URI->uri_string;
@@ -738,8 +736,7 @@ public function _display_cache(&$CFG, &$URI)
 	public function delete_cache($uri = '')
 	{
 		$CI =& get_instance();
-		$path = $CI->config->item('cache_path');
-		$cache_path = ($path === '') ? APPPATH.'cache'.DIRECTORY_SEPARATOR : rtrim($path, '/\\').DIRECTORY_SEPARATOR;
+		$cache_path = $this->_get_cache_path($CI->config->item('cache_path'));
 
 		if ( ! is_dir($cache_path))
 		{
@@ -777,6 +774,19 @@ public function delete_cache($uri = '')
 
 	// --------------------------------------------------------------------
 
+	/**
+	 * Get cache path
+	 *
+	 * @param	string	$path	The configured cache_path value
+	 * @return	string	Cache directory path with a trailing directory separator
+	 */
+	protected function _get_cache_path($path)
+	{
+		return empty($path) ? APPPATH.'cache'.DIRECTORY_SEPARATOR : rtrim($path, '/\\').DIRECTORY_SEPARATOR;
+	}
+
+	// --------------------------------------------------------------------
+
 	/**
 	 * Set Cache Header
 	 *
diff --git a/system/helpers/captcha_helper.php b/system/helpers/captcha_helper.php
index 8d24ac93bdc..bade01724ea 100644
--- a/system/helpers/captcha_helper.php
+++ b/system/helpers/captcha_helper.php
@@ -133,8 +133,7 @@ function create_captcha($data)
 			@closedir($current_dir);
 
 			// This variable will later be used later to determine whether we write to disk or output a data:image URI
-			// %F is locale-independent, unlike float-to-string conversion on PHP < 8.0
-			$img_filename = sprintf('%.6F', $now).'.png';
+			$img_filename = $now.'.png';
 		}
 		else
 		{
@@ -346,20 +345,9 @@ function create_captcha($data)
 		}
 		else
 		{
-			// I don't see an easier way to get the image contents without writing to file
-			$buffer = fopen('php://memory', 'wb+');
-			imagepng($im, $buffer);
-			rewind($buffer);
-			$img_src = '';
-
-			// fread() will return an empty string (not FALSE) after the entire contents are read
-			while (strlen($read = fread($buffer, 4096)))
-			{
-				$img_src .= $read;
-			}
-
-			fclose($buffer);
-			$img_src = 'data:image/png;base64,'.base64_encode($img_src);
+			ob_start();
+			imagepng($im);
+			$img_src = 'data:image/png;base64,'.base64_encode(ob_get_clean());
 		}
 
 		$img_class = trim($img_class);
diff --git a/system/libraries/Cache/drivers/Cache_file.php b/system/libraries/Cache/drivers/Cache_file.php
index 3a4be98a9ba..8dabac9dec8 100644
--- a/system/libraries/Cache/drivers/Cache_file.php
+++ b/system/libraries/Cache/drivers/Cache_file.php
@@ -66,7 +66,7 @@ public function __construct()
 		$CI =& get_instance();
 		$CI->load->helper('file');
 		$path = $CI->config->item('cache_path');
-		$this->_cache_path = ($path === '') ? APPPATH.'cache/' : $path;
+		$this->_cache_path = empty($path) ? APPPATH.'cache'.DIRECTORY_SEPARATOR : rtrim($path, '/\\').DIRECTORY_SEPARATOR;
 	}
 
 	// ------------------------------------------------------------------------
diff --git a/system/libraries/Cache/drivers/Cache_redis.php b/system/libraries/Cache/drivers/Cache_redis.php
index ac92d5ad8e1..2dd68e6deba 100644
--- a/system/libraries/Cache/drivers/Cache_redis.php
+++ b/system/libraries/Cache/drivers/Cache_redis.php
@@ -163,11 +163,17 @@ public function get($key)
 	{
 		$data = $this->_redis->hMGet($key, array('__ci_type', '__ci_value'));
 
-		if ($data === FALSE || $this->_redis->sIsMember('_ci_redis_serialized', $key))
+		if ($this->_redis->sIsMember('_ci_redis_serialized', $key))
 		{
 			return FALSE;
 		}
 
+		// Also serves scalars that 3.1.x cached as plain strings
+		if ($data === FALSE)
+		{
+			return $this->_redis->get($key);
+		}
+
 		switch ($data['__ci_type'])
 		{
 			case 'array':
@@ -261,15 +267,7 @@ public function delete($key)
 	 */
 	public function increment($id, $offset = 1)
 	{
-		$value = $this->_redis->hIncrBy($id, '__ci_value', $offset);
-
-		if ($value !== FALSE)
-		{
-			$this->_redis->hSet($id, '__ci_type', 'integer');
-			return $value;
-		}
-
-		return FALSE;
+		return $this->_increment($id, $offset);
 	}
 
 	// ------------------------------------------------------------------------
@@ -283,15 +281,29 @@ public function increment($id, $offset = 1)
 	 */
 	public function decrement($id, $offset = 1)
 	{
-		$value = $this->_redis->hIncrBy($id, '__ci_value', -$offset);
+		return $this->_increment($id, -$offset);
+	}
 
-		if ($value !== FALSE)
+	// ------------------------------------------------------------------------
+
+	/**
+	 * Add to a counter
+	 *
+	 * @param	string	$id	Cache ID
+	 * @param	int	$offset	Amount to add (negative to subtract)
+	 * @return	mixed	New value on success or FALSE on failure
+	 */
+	protected function _increment($id, $offset)
+	{
+		$value = $this->_redis->incrBy($id, $offset);
+
+		if ($value === FALSE)
 		{
-			$this->_redis->hSet($id, '__ci_type', 'integer');
-			return $value;
+			$value = $this->_redis->hIncrBy($id, '__ci_value', $offset);
+			$value === FALSE OR $this->_redis->hSet($id, '__ci_type', 'integer');
 		}
 
-		return FALSE;
+		return $value;
 	}
 
 	// ------------------------------------------------------------------------
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 48a9d035b16..9896740e6f1 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -587,8 +587,6 @@ protected function _reduce_array($array, $keys, $i = 0)
 	/**
 	 * Re-populate the _POST array with our finalized and processed data
 	 *
-	 * Arrays require bracket notation or an explicit is_array rule.
-	 *
 	 * @return	void
 	 */
 	protected function _reset_data_array(&$data)
diff --git a/system/libraries/Image_lib.php b/system/libraries/Image_lib.php
index 948d084f9c4..1f3c4815aeb 100644
--- a/system/libraries/Image_lib.php
+++ b/system/libraries/Image_lib.php
@@ -1251,8 +1251,7 @@ public function overlay_watermark()
 			imagecopymerge($src_img, $wm_img, $x_axis, $y_axis, 0, 0, $wm_width, $wm_height, $this->wm_opacity);
 		}
 
-		// We can preserve transparency for PNG images
-		if ($this->image_type === 3)
+		if ($this->image_type === 3 OR $this->image_type === 18)
 		{
 			imagealphablending($src_img, FALSE);
 			imagesavealpha($src_img, TRUE);
@@ -1425,8 +1424,7 @@ public function text_watermark()
 			imagestring($src_img, $this->wm_font_size, $x_axis, $y_axis, $this->wm_text, $txt_color);
 		}
 
-		// We can preserve transparency for PNG images
-		if ($this->image_type === 3)
+		if ($this->image_type === 3 OR $this->image_type === 18)
 		{
 			imagealphablending($src_img, FALSE);
 			imagesavealpha($src_img, TRUE);
diff --git a/system/libraries/Session/drivers/Session_redis_driver.php b/system/libraries/Session/drivers/Session_redis_driver.php
index bc25293509a..e20413a05f4 100644
--- a/system/libraries/Session/drivers/Session_redis_driver.php
+++ b/system/libraries/Session/drivers/Session_redis_driver.php
@@ -134,15 +134,17 @@ public function __construct(&$params)
 		{
 			log_message('error', 'Session: No Redis save path configured.');
 		}
-		elseif (preg_match('#^unix://([^\?]+)(?<options>\?.+)?$#', $this->_config['save_path'], $matches))
+		elseif (preg_match('#^unix://([^\?]+)(?<options>\?.+)?$#i', $this->_config['save_path'], $matches))
 		{
 			$save_path = array('path' => $matches[1]);
 		}
-		elseif (preg_match('#^(?:(tcp|tls|ssl)://)?([^:?]+)(?:\:(\d+))?(?<options>\?.+)?#', $this->_config['save_path'], $matches))
+		elseif (preg_match('#^(?:(tcp|tls|ssl)://)?([^:?]+)(?:\:(\d+))?(?<options>\?.+)?#i', $this->_config['save_path'], $matches))
 		{
+			$scheme = strtolower($matches[1]);
+
 			// phpredis needs the tls:// or ssl:// scheme in the host to enable encryption; tcp:// is the default
 			$save_path = array(
-				'host'    => (in_array($matches[1], array('tls', 'ssl'), TRUE) ? $matches[1].'://' : '').$matches[2],
+				'host'    => (in_array($scheme, array('tls', 'ssl'), TRUE) ? $scheme.'://' : '').$matches[2],
 				'port'    => empty($matches[3]) ? NULL : $matches[3],
 				'timeout' => 0.0 // We always pass this to Redis::connect(), so it needs to exist
 			);
diff --git a/tests/codeigniter/core/Output_test.php b/tests/codeigniter/core/Output_test.php
index 8c99c1fc5fe..7de57afa57c 100644
--- a/tests/codeigniter/core/Output_test.php
+++ b/tests/codeigniter/core/Output_test.php
@@ -60,4 +60,35 @@ public function test_get_header()
 		);
 	}
 
+	// --------------------------------------------------------------------
+
+	public function test_delete_cache_without_trailing_slash()
+	{
+		$this->ci_set_config('cache_path', APPPATH.'pagecache');
+		$this->ci_set_config('base_url', 'http://example.com/');
+		$this->ci_set_config('index_page', 'index.php');
+
+		$cache_file = md5('http://example.com/index.php/foo');
+		$dir = $this->ci_vfs_mkdir('pagecache', $this->ci_app_root);
+		vfsStream::newFile($cache_file)->at($dir)->setContent('cached');
+
+		$this->assertTrue($this->output->delete_cache('foo'));
+		$this->assertFalse($dir->hasChild($cache_file));
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_delete_cache_without_cache_path()
+	{
+		$this->ci_set_config('base_url', 'http://example.com/');
+		$this->ci_set_config('index_page', 'index.php');
+
+		$cache_file = md5('http://example.com/index.php/foo');
+		$dir = $this->ci_vfs_mkdir('cache', $this->ci_app_root);
+		vfsStream::newFile($cache_file)->at($dir)->setContent('cached');
+
+		$this->assertTrue($this->output->delete_cache('foo'));
+		$this->assertFalse($dir->hasChild($cache_file));
+	}
+
 }
diff --git a/tests/codeigniter/database/Postgre_forge_test.php b/tests/codeigniter/database/Postgre_forge_test.php
new file mode 100644
index 00000000000..03e8ffcd847
--- /dev/null
+++ b/tests/codeigniter/database/Postgre_forge_test.php
@@ -0,0 +1,56 @@
+<?php
+
+class Postgre_forge_test extends CI_TestCase {
+
+	/**
+	 * @dataProvider forge_provider
+	 */
+	public function test_modify_column_comments_renamed_column($forge_class)
+	{
+		$db = new Postgre_forge_db_stub();
+		$forge = new $forge_class($db);
+
+		$this->assertTrue($forge->modify_column('users', array(
+			'old_name' => array('name' => 'new_name', 'comment' => 'Renamed column')
+		)));
+
+		$this->assertSame(array(
+			'ALTER TABLE "users" RENAME COLUMN "old_name" TO "new_name"',
+			'COMMENT ON COLUMN "users"."new_name" IS \'Renamed column\''
+		), $db->queries);
+	}
+
+	public function forge_provider()
+	{
+		return array(array('CI_DB_postgre_forge'), array('CI_DB_pdo_pgsql_forge'));
+	}
+
+}
+
+class Postgre_forge_db_stub {
+
+	public $dbprefix = '';
+	public $db_debug = FALSE;
+	public $queries = array();
+
+	public function version()
+	{
+		return '15.0';
+	}
+
+	public function escape_identifiers($item)
+	{
+		return '"'.$item.'"';
+	}
+
+	public function escape($str)
+	{
+		return "'".str_replace("'", "''", $str)."'";
+	}
+
+	public function query($sql)
+	{
+		$this->queries[] = $sql;
+		return TRUE;
+	}
+}
diff --git a/tests/codeigniter/helpers/captcha_helper_test.php b/tests/codeigniter/helpers/captcha_helper_test.php
index f2d2599f539..7b4d4abf82c 100644
--- a/tests/codeigniter/helpers/captcha_helper_test.php
+++ b/tests/codeigniter/helpers/captcha_helper_test.php
@@ -38,14 +38,13 @@ public function tear_down()
 
 	// --------------------------------------------------------------------
 
-	public function test_create_captcha_writes_image_with_fractional_timestamp_filename()
+	public function test_create_captcha_names_image_after_time()
 	{
 		$captcha = $this->_create_captcha();
 
 		$this->assertTrue(is_array($captcha));
-		$this->assertEquals(1, preg_match('#^\d{10}\.\d{6}\.png$#', $captcha['filename']));
+		$this->assertSame($captcha['time'].'.png', $captcha['filename']);
 		$this->assertTrue(is_file($this->_img_path.$captcha['filename']));
-		$this->assertSame(sprintf('%.6F', $captcha['time']).'.png', $captcha['filename']);
 	}
 
 	// --------------------------------------------------------------------
@@ -148,21 +147,16 @@ public function test_create_captcha_respects_custom_expiration()
 
 	// --------------------------------------------------------------------
 
-	public function test_create_captcha_filename_is_locale_independent()
+	public function test_create_captcha_returns_data_uri_without_paths()
 	{
-		$original = setlocale(LC_NUMERIC, 0);
-		$locale = setlocale(LC_NUMERIC, 'de_DE.UTF-8', 'de_DE.utf8', 'de_DE', 'de-DE', 'German_Germany.1252', 'German');
+		$captcha = create_captcha(array('word' => 'test'));
 
-		if ($locale === FALSE)
-		{
-			$this->markTestSkipped('No locale with a comma decimal separator is available.');
-		}
-
-		$captcha = $this->_create_captcha();
-		setlocale(LC_NUMERIC, $original);
+		$this->assertTrue(is_array($captcha));
+		$this->assertNull($captcha['filename']);
+		$this->assertEquals(1, preg_match('#src="data:image/png;base64,([A-Za-z0-9+/=]+)"#', $captcha['image'], $match));
+		$this->assertSame("\x89PNG", substr(base64_decode($match[1]), 0, 4));
 
-		$this->assertEquals(1, preg_match('#^\d{10}\.\d{6}\.png$#', $captcha['filename']));
-		$this->assertTrue(is_file($this->_img_path.$captcha['filename']));
+		$this->assertFalse(create_captcha(array('word' => 'test', 'img_url' => 'http://example.com/captcha/')));
 	}
 
 	// --------------------------------------------------------------------
diff --git a/tests/codeigniter/libraries/Cache_file_test.php b/tests/codeigniter/libraries/Cache_file_test.php
new file mode 100644
index 00000000000..fa635316b15
--- /dev/null
+++ b/tests/codeigniter/libraries/Cache_file_test.php
@@ -0,0 +1,39 @@
+<?php
+
+class Cache_file_test extends CI_TestCase {
+
+	public function set_up()
+	{
+		class_exists('CI_Driver_Library', TRUE);
+		$this->helper('file');
+
+		$loader = $this->getMockBuilder('CI_Loader')->setMethods(array('helper'))->getMock();
+		$this->ci_instance_var('load', $loader);
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_cache_path_without_trailing_slash()
+	{
+		$this->ci_set_config('cache_path', APPPATH.'filecache');
+		$dir = $this->ci_vfs_mkdir('filecache', $this->ci_app_root);
+		$cache = new CI_Cache_file();
+
+		$this->assertTrue($cache->save('foo', 'bar'));
+		$this->assertTrue($dir->hasChild('foo'));
+		$this->assertEquals('bar', $cache->get('foo'));
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_cache_path_without_config_key()
+	{
+		$this->ci_set_config();
+		$dir = $this->ci_vfs_mkdir('cache', $this->ci_app_root);
+		$cache = new CI_Cache_file();
+
+		$this->assertTrue($cache->save('foo', 'bar'));
+		$this->assertTrue($dir->hasChild('foo'));
+	}
+
+}
diff --git a/tests/codeigniter/libraries/Cache_redis_test.php b/tests/codeigniter/libraries/Cache_redis_test.php
new file mode 100644
index 00000000000..814d0e63c7c
--- /dev/null
+++ b/tests/codeigniter/libraries/Cache_redis_test.php
@@ -0,0 +1,144 @@
+<?php
+
+class Cache_redis_test extends CI_TestCase {
+
+	public function set_up()
+	{
+		class_exists('CI_Driver_Library', TRUE);
+
+		$this->redis = new Cache_redis_server_stub();
+
+		$class = new ReflectionClass('CI_Cache_redis');
+		$this->cache = $class->newInstanceWithoutConstructor();
+
+		$property = new ReflectionProperty('CI_Cache_redis', '_redis');
+		if (PHP_VERSION_ID < 80100)
+		{
+			$property->setAccessible(TRUE);
+		}
+		$property->setValue($this->cache, $this->redis);
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_increment_creates_plain_counter()
+	{
+		$this->assertSame(1, $this->cache->increment('hits'));
+		$this->assertSame(3, $this->cache->increment('hits', 2));
+		$this->assertSame(2, $this->cache->decrement('hits'));
+
+		$this->assertSame('2', $this->redis->strings['hits']);
+		$this->assertEquals(2, $this->cache->get('hits'));
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_increment_existing_plain_counter()
+	{
+		$this->redis->strings['hits'] = '5';
+
+		$this->assertSame(6, $this->cache->increment('hits'));
+		$this->assertSame(4, $this->cache->decrement('hits', 2));
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_increment_saved_value()
+	{
+		$this->redis->hashes['hits'] = array('__ci_type' => 'integer', '__ci_value' => '5');
+
+		$this->assertSame(6, $this->cache->increment('hits'));
+		$this->assertSame(5, $this->cache->decrement('hits'));
+		$this->assertSame(5, $this->cache->get('hits'));
+	}
+
+	// --------------------------------------------------------------------
+
+	public function test_increment_non_numeric_value()
+	{
+		$this->redis->strings['name'] = 'bar';
+		$this->redis->hashes['data'] = array('__ci_type' => 'string', '__ci_value' => 'bar');
+
+		$this->assertFalse($this->cache->increment('name'));
+		$this->assertFalse($this->cache->increment('data'));
+		$this->assertSame('string', $this->redis->hashes['data']['__ci_type']);
+	}
+
+}
+
+class Cache_redis_server_stub {
+
+	public $strings = array();
+	public $hashes = array();
+
+	public function incrBy($key, $offset)
+	{
+		if (isset($this->hashes[$key]) OR (isset($this->strings[$key]) && ! ctype_digit(ltrim($this->strings[$key], '-'))))
+		{
+			return FALSE;
+		}
+
+		$value = (isset($this->strings[$key]) ? (int) $this->strings[$key] : 0) + $offset;
+		$this->strings[$key] = (string) $value;
+		return $value;
+	}
+
+	public function hIncrBy($key, $field, $offset)
+	{
+		if (isset($this->strings[$key]) OR (isset($this->hashes[$key][$field]) && ! ctype_digit(ltrim($this->hashes[$key][$field], '-'))))
+		{
+			return FALSE;
+		}
+
+		$value = (isset($this->hashes[$key][$field]) ? (int) $this->hashes[$key][$field] : 0) + $offset;
+		$this->hashes[$key][$field] = (string) $value;
+		return $value;
+	}
+
+	public function hSet($key, $field, $value)
+	{
+		if (isset($this->strings[$key]))
+		{
+			return FALSE;
+		}
+
+		$this->hashes[$key][$field] = (string) $value;
+		return 1;
+	}
+
+	public function hMGet($key, $fields)
+	{
+		if (isset($this->strings[$key]))
+		{
+			return FALSE;
+		}
+
+		$values = array();
+		foreach ($fields as $field)
+		{
+			$values[$field] = isset($this->hashes[$key][$field]) ? $this->hashes[$key][$field] : FALSE;
+		}
+
+		return $values;
+	}
+
+	public function get($key)
+	{
+		if (isset($this->hashes[$key]))
+		{
+			return FALSE;
+		}
+
+		return isset($this->strings[$key]) ? $this->strings[$key] : FALSE;
+	}
+
+	public function sIsMember($key, $member)
+	{
+		return FALSE;
+	}
+
+	public function close()
+	{
+		return TRUE;
+	}
+}
diff --git a/tests/codeigniter/libraries/Form_validation_test.php b/tests/codeigniter/libraries/Form_validation_test.php
index 1bafd50c350..6e1029cc6b7 100644
--- a/tests/codeigniter/libraries/Form_validation_test.php
+++ b/tests/codeigniter/libraries/Form_validation_test.php
@@ -642,6 +642,104 @@ public function test_validated_data_assignment()
 		$_POST = array();
 	}
 
+	public function test_set_rules_null_label_uses_field_name()
+	{
+		$_POST = array('email' => '');
+		$this->form_validation->set_message('required', 'The {field} field is required.');
+		$this->form_validation->set_rules('email', NULL, 'required');
+
+		$this->assertFalse($this->form_validation->run());
+		$this->assertEquals('<p>The email field is required.</p>', $this->form_validation->error('email'));
+
+		$_POST = array();
+	}
+
+	public function test_is_array_rule_on_bracket_field()
+	{
+		$_POST = array('tags' => array('a', 'b'));
+		$this->form_validation->set_rules('tags[]', 'Tags', 'required|is_array');
+		$this->assertTrue($this->form_validation->run());
+
+		$this->form_validation->reset_validation();
+		$this->form_validation->set_data(array('tags' => array()));
+		$this->form_validation->set_rules('tags[]', 'Tags', 'required|is_array');
+		$this->assertFalse($this->form_validation->run());
+
+		$_POST = array();
+	}
+
+	public function test_is_array_rule_on_bracket_field_passes_whole_array_to_callable()
+	{
+		$seen = NULL;
+		$_POST = array('tags' => array('a', 'b'));
+		$this->form_validation->set_rules('tags[]', 'Tags', array(
+			'is_array',
+			array('capture', function ($value) use (&$seen) {
+				$seen = $value;
+				return TRUE;
+			})
+		));
+
+		$this->assertTrue($this->form_validation->run());
+		$this->assertEquals(array('a', 'b'), $seen);
+
+		$_POST = array();
+	}
+
+	public function test_is_array_rule_on_keyed_field()
+	{
+		$_POST = array('user' => array('roles' => array('admin', 'editor')));
+		$this->form_validation->set_rules('user[roles]', 'Roles', 'required|is_array');
+
+		$this->assertTrue($this->form_validation->run());
+		$this->assertEquals(array('admin', 'editor'), $_POST['user']['roles']);
+
+		$_POST = array();
+	}
+
+	public function test_is_array_rule_keeps_array_after_run()
+	{
+		$_POST = array('tags' => array('a', 'b'));
+		$this->form_validation->set_rules('tags', 'Tags', 'required|is_array');
+
+		$this->assertTrue($this->form_validation->run());
+		$this->assertEquals(array('a', 'b'), $_POST['tags']);
+
+		$this->form_validation->reset_validation();
+		$this->form_validation->set_data(array('tags' => array('a', 'b')));
+		$this->form_validation->set_rules('tags', 'Tags', 'is_array');
+		$data_processed = NULL;
+
+		$this->assertTrue($this->form_validation->run('', $data_processed));
+		$this->assertEquals(array('a', 'b'), $data_processed['tags']);
+
+		$_POST = array();
+	}
+
+	public function test_array_input_without_is_array_rule()
+	{
+		$_POST = array('name' => array('x'), 'other' => 'y');
+		$this->form_validation->set_rules('name', 'Name', 'alpha');
+		$this->form_validation->set_rules('other', 'Other', 'required');
+
+		$this->assertTrue($this->form_validation->run());
+		$this->assertNull($_POST['name']);
+
+		$this->assertFalse($this->run_rules(
+			array(array('field' => 'ids[]', 'label' => 'IDs', 'rules' => 'numeric')),
+			array('ids' => array('1', 'x'))
+		));
+
+		$this->form_validation->reset_validation();
+		$_POST = array('names' => array(' a ', ' b '));
+		$this->form_validation->set_rules('names[]', 'Names', 'trim|required');
+
+		$this->assertTrue($this->form_validation->run());
+		$this->assertEquals(array('a', 'b'), $_POST['names']);
+
+		$_POST = array();
+	}
+
 	/**
 	 * Run rules
 	 *
diff --git a/tests/codeigniter/libraries/Useragent_test.php b/tests/codeigniter/libraries/Useragent_test.php
index 8c5b28b9f7c..7ffe9fc8dc0 100644
--- a/tests/codeigniter/libraries/Useragent_test.php
+++ b/tests/codeigniter/libraries/Useragent_test.php
@@ -142,4 +142,11 @@ public function test_edge()
 		$this->assertEquals('Edge', $this->agent->browser());
 	}
 
+	public function test_vivaldi()
+	{
+		$this->agent->parse('Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36 Vivaldi/6.5.3206.48');
+		$this->assertEquals('Vivaldi', $this->agent->browser());
+		$this->assertEquals('6.5.3206.48', $this->agent->version());
+	}
+
 }
\ No newline at end of file
diff --git a/user_guide_src/source/installation/upgrade_320.rst b/user_guide_src/source/installation/upgrade_320.rst
index 2226d8588ca..170acc01274 100644
--- a/user_guide_src/source/installation/upgrade_320.rst
+++ b/user_guide_src/source/installation/upgrade_320.rst
@@ -270,3 +270,62 @@ entries by key needs review.
 .. note:: In 3.2-dev, this function was broken and returned entries holding
 	only a ``relative_path`` key, so there is nothing to migrate if you are
 	coming from there.
+
+Step 16: Replace config/user_agents.php and config/mimes.php
+============================================================
+
+These config files have received some updates. Please copy them to
+*application/config/user_agents.php* and *application/config/mimes.php*.
+
+Step 17: Check form validation rules for array fields
+=====================================================
+
+This only affects form fields that receive arrays. If you don't validate
+array input, you can skip this step.
+
+If you are upgrading from 3.1.x, check validation rules for field names
+without brackets, such as ``tags``. Submitted arrays are now set to
+``NULL`` in ``$_POST`` after a successful ``run()``; 3.1.x kept them in
+``$_POST``. Add ``is_array`` to accept and keep the array, or use ``tags[]``
+to validate each element.
+
+If you are upgrading from 3.2-dev, check rules that include ``is_array``
+for bracketed field names such as ``items[]``. Rules and callbacks now
+receive the whole array; previously only the first element was validated
+and passed to callbacks. See :ref:`using-arrays-as-field-names`.
+
+Step 18: Check full-page caching with a custom cache_path
+=========================================================
+
+If you set ``$config['cache_path']`` without a trailing slash, such as
+``/var/cache/ci``, cached pages are now served. Previously, cache files
+were written but never read. This does not affect configurations where
+``cache_path`` is empty or already ends with a slash.
+
+Before upgrading, check that pages calling ``$this->output->cache()`` do
+not include per-user content, such as account details or CSRF tokens.
+Cached output can be served to other visitors. See
+:doc:`Web Page Caching <../general/caching>`.
+
+Step 19: Check CAPTCHA image handling
+=====================================
+
+The :doc:`CAPTCHA Helper <../helpers/captcha_helper>` function
+:php:func:`create_captcha()` now correctly removes expired images from
+``img_path`` when it runs. It matches filenames consisting of a 10-digit
+timestamp with an optional fractional part (``.`` or ``,`` separator),
+followed by ``.png`` or ``.jpg`` (case-insensitive). Keep ``img_path``
+dedicated to CAPTCHA images: any matching file is deleted after
+``expiration`` seconds (default 7200). Other files are left alone.
+
+If you are upgrading from 3.1.x, check code that assumes JPEG output.
+Since 3.2-dev, ``create_captcha()`` always writes PNG files; 3.1.x used
+JPEG when ``imagejpeg()`` was available. Replace filenames built from
+``$cap['time']`` plus ``.jpg`` with the returned ``$cap['filename']``,
+which contains the exact filename (``$cap['time']`` plus ``.png``).
+
+Omitting both ``img_path`` and ``img_url`` returns the image inline as a
+``data:image/png;base64,...`` URI again, as described in the CAPTCHA helper
+documentation. This mode was added in 3.2-dev in 2017, but a 2020 merge
+accidentally disabled it, causing ``create_captcha()`` to return ``FALSE``
+instead.
diff --git a/user_guide_src/source/libraries/form_validation.rst b/user_guide_src/source/libraries/form_validation.rst
index 5f30817eb1e..cc329cda057 100644
--- a/user_guide_src/source/libraries/form_validation.rst
+++ b/user_guide_src/source/libraries/form_validation.rst
@@ -957,6 +957,21 @@ When you use a helper function you'll include the bracket as well::
 
 	<?php echo form_error('options[color][]'); ?>
 
+Without the ``is_array`` rule, rules for bracketed field names run once
+per array element. With ``is_array``, every rule in the list, including
+callbacks and callables, receives the whole array instead. This applies
+to field names with or without brackets, such as ``tags``, ``tags[]``
+and ``user[roles]``::
+
+	$this->form_validation->set_rules('tags', 'Tags', 'required|is_array');
+
+The ``required`` rule combined with ``is_array`` rejects an empty array.
+
+For field names without brackets, array input is otherwise treated as an
+empty value. After a successful ``run()``, that value is set to ``NULL``
+in ``$_POST``, or in the output variable passed as the second parameter
+to ``run()``. Adding ``is_array`` accepts and keeps the array.
+
 
 **************
 Rule Reference
@@ -969,6 +984,8 @@ use:
 Rule                      Parameter  Description                                                                                   Example
 ========================= ========== ============================================================================================= =======================
 **required**              No         Returns FALSE if the form element is empty.
+**is_array**              No         Returns FALSE if the form element is not an array.
+                                     See :ref:`using-arrays-as-field-names` for details on validating entire arrays.
 **matches**               Yes        Returns FALSE if the form element does not match the one in the parameter.                    matches[form_item]
 **regex_match**           Yes        Returns FALSE if the form element does not match the regular expression.                      regex_match[/regex/]
 **differs**               Yes        Returns FALSE if the form element does not differ from the one in the parameter.              differs[form_item]
@@ -1009,8 +1026,8 @@ Rule                      Parameter  Description
 **valid_base64**          No         Returns FALSE if the supplied string contains anything other than valid Base64 characters.
 ========================= ========== ============================================================================================= =======================
 
-.. note:: These rules can also be called as discrete methods. For
-	example::
+.. note:: These rules can also be called as discrete methods, except for
+	``is_array``, which is a native PHP function. For example::
 
 		$this->form_validation->required($string);