This page provides info about the escape character in PHP
This is an example that needs no slash because no characters need to be escaped.
This line does need a slash because it was written by Mr. O'Reilly.
The escape character (backslash) is used when we want to print out a character as part of a string
when it would otherwise be interpreted as something else. In the example above, it would be interpreted
as the end of the string and cause the code to crash because there would be a mismatch of opening
and closing quotes.