* https://wiki.selfhtml.org/wiki/PHP/Tutorials/Einstieg/Grundlagen#Einfache_Typen_und_ihre_Literale
  * https://www.php.net/manual/de/language.types.string.php
  * https://www.php.net/manual/de/language.operators.string.php
  * https://www.php.net/manual/de/ref.strings.php
  * https://www.php.net/manual/de/function.printf.php