Several changes have been made in this commit, which together with the previous commits result in version 2.0 (database update required):v2.0

+ Implemented [core]: A new database field has been added to all tables to define optional "arguments" for a page, post or user through the content editor. These arguments will be parsed into key->value pairs and can be used within templates to do something special. Please read the wiki of this repository for further information about this new feature.
+ Bugfix [core]: The function "makeSlugURL" had not convert uppercase umlauts to lowercase because "strtolower" was used instead of the multibyte equivalent "mb_strtolower".
+ Optimization [core]: The first regular expression within the function "makeSlugURL" has been optimized (checking for uppercase characters at this point is unnecessary because $string is only lowercase).
+ Optimization [all templates]: Markup for the pagination.php has been simplified (a little bit).
+ Optimization [admin template]: The javascript for the arrow key navigation has been outsourced to the main.js file.
+ Optimization [admin template]: The javascript file will now be included with the "defer" attribute.
+ Optimization [standard template]: Some language variables have been changed.

Database update to version 2.0 (no existing data will be lost or changed):

ALTER TABLE `page` ADD `argv` VARCHAR(100) NULL DEFAULT NULL AFTER `body`;
ALTER TABLE `post` ADD `argv` VARCHAR(100) NULL DEFAULT NULL AFTER `body`;
ALTER TABLE `user` ADD `argv` VARCHAR(100) NULL DEFAULT NULL AFTER `body`;

5 files changed, 26 insertions, 2 deletions

diff --git a/core/functions.php b/core/functions.php
index c6bdb1e..2e36524 100644
--- a/core/functions.php
+++ b/core/functions.php
@@ -90,6 +90,7 @@ function generateItemData(Item $Item): array {
 		'ID'  => $Item->getID(),
 		'URL' => $Item->getURL(),
 		'GUID' => $Item->getGUID(),
+		'ARGV' => $Item->getArguments(),
 
 		'PREV' => FALSE,
 		'NEXT' => FALSE,
@@ -108,6 +109,7 @@ function generateItemData(Item $Item): array {
 			'SLUG' => $Item->attr('slug'),
 			'NAME' => $Item->attr('name'),
 			'BODY' => $Item->attr('body'),
+			'ARGV' => $Item->attr('argv'),
 			'TIME_INSERT' => $Item->attr('time_insert'),
 			'TIME_UPDATE' => $Item->attr('time_update')
 		]
@@ -136,6 +138,7 @@ function generateUserItemData(User\Item $User): array {
 		'ID'  => $User->getID(),
 		'URL' => $User->getURL(),
 		'GUID' => $User->getGUID(),
+		'ARGV' => $User->getArguments(),
 
 		'PREV' => FALSE,
 		'NEXT' => FALSE,
@@ -152,6 +155,7 @@ function generateUserItemData(User\Item $User): array {
 		'ATTR' => [
 			'SLUG' => $User->attr('slug'),
 			'BODY' => $User->attr('body'),
+			'ARGV' => $User->attr('argv'),
 			'USERNAME' => $User->attr('username'),
 			'FULLNAME' => $User->attr('fullname'),
 			'MAILADDR' => $User->attr('mailaddr'),
@@ -323,9 +327,9 @@ function description($string, $length = 200, $replace = ' […]') {
 # Generate a valid slug URL part from a string
 #===============================================================================
 function makeSlugURL($string) {
-	$string = strtolower($string);
+	$string = mb_strtolower($string);
 	$string = str_replace(['ä', 'ö', 'ü', 'ß'], ['ae', 'oe', 'ue', 'ss'], $string);
-	$string = preg_replace('/[^a-zA-Z0-9\-]/', '-', $string);
+	$string = preg_replace('/[^a-z0-9\-]/', '-', $string);
 	$string = preg_replace('/-+/', '-', $string);
 
 	return trim($string, '-');
diff --git a/core/namespace/Item.php b/core/namespace/Item.php
index f3b6ceb..426dd2a 100644
--- a/core/namespace/Item.php
+++ b/core/namespace/Item.php
@@ -102,6 +102,23 @@ abstract class Item implements ItemInterface {
 	}
 
 	#===============================================================================
+	# Return parsed arguments
+	#===============================================================================
+	public function getArguments(): array {
+		if($argv = $this->Attribute->get('argv')) {
+			foreach(explode('|', rtrim($argv, '|')) as $delimeter) {
+				$part = explode('=', $delimeter);
+
+				if(!empty($part[0])) {
+					$arguments[strtoupper($part[0])] = $part[1] ?? TRUE;
+				}
+			}
+		}
+
+		return $arguments ?? [];
+	}
+
+	#===============================================================================
 	# Return previous item ID
 	#===============================================================================
 	public function getPrevID(): int {
diff --git a/core/namespace/Page/Attribute.php b/core/namespace/Page/Attribute.php
index c12a2c8..b1c4e01 100644
--- a/core/namespace/Page/Attribute.php
+++ b/core/namespace/Page/Attribute.php
@@ -11,6 +11,7 @@ class Attribute extends \Attribute {
 	protected $slug = FALSE;
 	protected $name = FALSE;
 	protected $body = FALSE;
+	protected $argv = FALSE;
 	protected $time_insert = FALSE;
 	protected $time_update = FALSE;
 
diff --git a/core/namespace/Post/Attribute.php b/core/namespace/Post/Attribute.php
index 6f20183..73af3a2 100644
--- a/core/namespace/Post/Attribute.php
+++ b/core/namespace/Post/Attribute.php
@@ -11,6 +11,7 @@ class Attribute extends \Attribute {
 	protected $slug = FALSE;
 	protected $name = FALSE;
 	protected $body = FALSE;
+	protected $argv = FALSE;
 	protected $time_insert = FALSE;
 	protected $time_update = FALSE;
 
diff --git a/core/namespace/User/Attribute.php b/core/namespace/User/Attribute.php
index b161fa9..c83fdfc 100644
--- a/core/namespace/User/Attribute.php
+++ b/core/namespace/User/Attribute.php
@@ -13,6 +13,7 @@ class Attribute extends \Attribute {
 	protected $fullname = FALSE;
 	protected $mailaddr = FALSE;
 	protected $body     = FALSE;
+	protected $argv     = FALSE;
 	protected $time_insert = FALSE;
 	protected $time_update = FALSE;