It is suggested that the delimiter is passed to preg_quote

Just so it can handle escaping properly. Although, I don’t think that really matters in this case since exclamation marks are not valid in function names.

Modules/Tag/Traits/TaggableTrait.php

@@ -166,16 +166,16 @@ trait TaggableTrait
         // Convert all dashes/underscores into separator
         $flip = $separator == '-' ? '_' : '-';
 
-        $name = preg_replace('!['.preg_quote($flip).']+!u', $separator, $name);
+        $name = preg_replace('![' . preg_quote($flip, '!') . ']+!u', $separator, $name);
 
         // Replace @ with the word 'at'
-        $name = str_replace('@', $separator.'at'.$separator, $name);
+        $name = str_replace('@', $separator . 'at' . $separator, $name);
 
         // Remove all characters that are not the separator, letters, numbers, or whitespace.
-        $name = preg_replace('![^'.preg_quote($separator).'\pL\pN\s]+!u', '', mb_strtolower($name));
+        $name = preg_replace('![^' . preg_quote($separator, '!') . '\pL\pN\s]+!u', '', mb_strtolower($name));
 
         // Replace all separator characters and whitespace by a single separator
-        $name = preg_replace('!['.preg_quote($separator).'\s]+!u', $separator, $name);
+        $name = preg_replace('![' . preg_quote($separator, '!') . '\s]+!u', $separator, $name);
 
         return trim($name, $separator);
     }