The :.\+*?[^]$(){}=!<>|:-# letters are special characters that make regular expressions work. If you want to match one of these characters you need to write a backslash in front of that character in the pattern. For example, if you want to match a “+” character, you write “\+” in the pattern. You can escape special characters manually by placing a backslash in front of each character you want to match, or you can the use preg_quote() function to escape special characters automatically. In this tutorial, you’ll also learn a technique that helps you to avoid escaping special characters.