Entry Level PHP Web Application Development/Our First Programs: Hello, World!/SQS-Answer
A single-quoted string (also known as a single quoted string literal, because it is a value that means exactly what it looks like) has the purpose of including a string verbatim into a program. Single-quoted strings are not inspected by the PHP interpreter for variables to perform substitution in; for example, the string
'$foo on you' will appear as
$foo on you when output to the user’s web browser.