Quotes
Variables are interpreted and replaced, but only with double quotes.
$a = 4;
echo '$a'; // $a
echo "$a"; // 4
Herodoc
Herodoc format is used for formating on multiple lines.
/**
* Herodoc strings
*
* It is used for formating on multiple lines.
* You can use quotes without escaping.
*
* The closing identifier must contain no characters, except a semicolon (;)
* The first character after the closing identifier must be a newline.
*/
$who = "John";
$output = <<<TEST
She said "This is $who's test"
on multiple rows
TEST;
echo nl2br($output);
/*
She said "This is John's test"
on multiple rows
*/