diff --git a/functions.php b/functions.php
index db00cde..f7dda0d 100644
--- a/functions.php
+++ b/functions.php
@@ -8,14 +8,14 @@
 /**
  * Browsersprache ermitteln
  *
- * @param array  $allowed_languages Array of allowed languages
- * @param string $default_language  Language code of the default language
- * @param string $lang_variable     Already set language variable
- * @param bool   $strict_mode       Whether to demand de (false) or de-de
+ * @param array       $allowed_languages Array of allowed languages.
+ * @param string      $default_language  Language code of the default language.
+ * @param string|null $lang_variable     Already set language variable.
+ * @param boolean     $strict_mode       Whether to demand de (false) or de-de.
  *
  * @return string
  */
-function lang_getfrombrowser($allowed_languages, $default_language, $lang_variable = null, $strict_mode = true) {
+function lang_getfrombrowser(array $allowed_languages, string $default_language, $lang_variable = null, bool $strict_mode = true) {
     // $_SERVER['HTTP_ACCEPT_LANGUAGE'] verwenden, wenn keine Sprachvariable mitgegeben wurde
     if ($lang_variable === null) {
         if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) $lang_variable = $_SERVER['HTTP_ACCEPT_LANGUAGE'];
@@ -37,8 +37,7 @@ function lang_getfrombrowser($allowed_languages, $default_language, $lang_variab
     // Nun alle mitgegebenen Sprachen abarbeiten
     foreach ($accepted_languages as $accepted_language) {
         // Alle Infos über diese Sprache rausholen
-        $res = preg_match('/^([a-z]{1,8}(?:-[a-z]{1,8})*)'.
-            '(?:;\s*q=(0(?:\.[0-9]{1,3})?|1(?:\.0{1,3})?))?$/i', $accepted_language, $matches
+        $res = preg_match('/^([a-z]{1,8}(?:-[a-z]{1,8})*)' . '(?:;\s*q=(0(?:\.[0-9]{1,3})?|1(?:\.0{1,3})?))?$/i', $accepted_language, $matches
         );
 
         // war die Syntax gültig?
@@ -93,7 +92,7 @@ function lang_getfrombrowser($allowed_languages, $default_language, $lang_variab
  *
  * @return void
  */
-function ensureDir($filepath) {
+function ensureDir(string $filepath) {
     if (!is_dir($filepath)) mkdir($filepath);
 }
 
@@ -104,7 +103,7 @@ function ensureDir($filepath) {
  *
  * @return void
  */
-function ensureJson($filepath) {
+function ensureJson(string $filepath) {
 
     if (!file_exists($filepath) or filesize($filepath) < 2) {
         file_put_contents($filepath, "[]");
@@ -134,21 +133,21 @@ function ensureEnvironment() {
 /**
  * Function transform escapes a string for printing in TeX
  *
- * @param string $transform String to transform
+ * @param string $transform String to transform.
  *
  * @return string
  */
-function transform($transform) {
+function transform(string $transform):string {
 
     $transform = preg_replace('#<br>#', ' ', $transform);
     $transform = preg_replace('#</br>#', ' ', $transform);
     $transform = preg_replace('#<br />#', ' ', $transform);
     $transform = preg_replace('#&rsquo;#', '\'', $transform);
-    $transform = preg_replace('#'.chr(11).'#', ' ', $transform);
+    $transform = preg_replace('#' . chr(11) . '#', ' ', $transform);
     $transform = preg_replace('#&quot;#', '"', $transform);
     $transform = preg_replace('#&amp;#', '&', $transform);
     $transform = preg_replace('#•#', '&#8226;', $transform);
-    $transform = preg_replace('#'.chr(9).'#', '', $transform);
+    $transform = preg_replace('#' . chr(9) . '#', '', $transform);
     $transform = str_replace('&', '\\&', $transform);
     $transform = str_replace('{', '\\{', $transform);
     $transform = str_replace('}', '\\}', $transform);
@@ -179,7 +178,7 @@ function transform($transform) {
     $transform = preg_replace('#è#', '&#232;', $transform);
 
     foreach (array("[", "]") as $toescape)
-        $transform = str_replace ($toescape, "$".$toescape."$", $transform);
+        $transform = str_replace ($toescape, "$" . $toescape . "$", $transform);
 
     $transform = html_entity_decode($transform, ENT_QUOTES, "utf-8" );
     return $transform;
@@ -192,7 +191,7 @@ function transform($transform) {
  *
  * @return string[]
  */
-function scanDirConts($folder) {
+function scanDirConts(string $folder) {
     return array_values(array_diff(scandir($folder), [".", "..", ".git"]));
 }
 
@@ -206,8 +205,8 @@ function scanDirConts($folder) {
  *
  * @return void
  */
-function copyFolder($from, $to) {
-    mkdir ($to);
+function copyFolder(string $from, string $to) {
+    mkdir($to);
     foreach (array_diff(scandir("$from"), [".", ".."]) as $file) {
         copy("$from/$file", "$to/$file");
     }
@@ -220,7 +219,7 @@ function copyFolder($from, $to) {
  *
  * @return void
  */
-function removeFolder($folder) {
+function removeFolder(string $folder) {
     foreach (array_diff(scandir("$folder"), [".", ".."]) as $file) {
         if (is_dir("$folder/$file")) removeFolder("$folder/$file");
         else unlink("$folder/$file");
@@ -237,7 +236,7 @@ function removeFolder($folder) {
  *
  * @return boolean
  */
-function removeFolderGently($folder, $exclude) {
+function removeFolderGently(string $folder, string $exclude) {
     foreach (array_diff(scandir("$folder"), [".", ".."]) as $file) {
         if (time() - filemtime("$folder/$file") < 10 and $file != $exclude) continue;
         if (is_dir("$folder/$file")) $output = removeFolder("$folder/$file");
@@ -254,13 +253,13 @@ function removeFolderGently($folder, $exclude) {
  * @param string  $folder      Determines the folder (say, template) to use for PDF generation.
  * @param string  $texFilename Name of the TeX file. Used without its ending.
  * @param string  $filename    Filename as it should be shown to the user.
- * @param boolean $pdfSettings Additional parameters to use \def for.
- * @param boolean $lang        Language. Optional.
+ * @param array   $pdfSettings Additional parameters to use \def for.
+ * @param string  $lang        Language. Optional.
  * @param boolean $debug       Enables/disables debug mode. Optional.
  *
  * @return void
  */
-function runPDF($folder, $texFilename, $filename, $pdfSettings, $lang = "de", $debug = false) {
+function runPDF(string $folder, string $texFilename, string $filename, array $pdfSettings, string $lang = "de", bool $debug = false) {
 
     if (!is_dir("./tmp")) mkdir("./tmp");
 
@@ -316,14 +315,14 @@ function runPDF($folder, $texFilename, $filename, $pdfSettings, $lang = "de", $d
  *
  * @param string $title          Title of the page.
  * @param string $contents       Page contents.
- * @param string $lang           Language. Optional
+ * @param string $lang           Language. Optional.
  * @param array  $availableLangs Page description. Optional.
  * @param string $descriptions   Page description. Optional.
  * @param string $pdfLink        Link to brochure. Optional.
  *
  * @return string
  */
-function printHTMLPage(string $title, string $contents, string $lang = "en", array $availableLangs = ["en"], string $descriptions = "", $pdfLink = "brochure") {
+function printHTMLPage(string $title, string $contents, string $lang = "en", array $availableLangs = ["en"], string $descriptions = "", string $pdfLink = "brochure"):string {
 
     $output = '<!DOCTYPE html>
 <html lang="' . $lang . '" id="' . str_replace(":", "", str_replace(" ", "", $title)) . '">
@@ -336,9 +335,9 @@ function printHTMLPage(string $title, string $contents, string $lang = "en", arr
     <link rel="shortcut icon" sizes="16x16 32x32" href="./media/mdlogo-32px.png" />
     <link rel="shortcut icon" sizes="64x64" href="./media/mdlogo-64px.png" /><link rel="stylesheet" type="text/css" href="css/main.css">
 
-    <meta name="twitter:title" content="' . $title. '" />
-    <meta property="og:title" content="' . $title. '" />
-    <title>' . $title. '</title>
+    <meta name="twitter:title" content="' . $title . '" />
+    <meta property="og:title" content="' . $title . '" />
+    <title>' . $title . '</title>
 
     <meta name="twitter:card" content="summary" />
     <meta name="twitter:site" content="@museumdigital" />