I don’t know why this took me so long, but I just discovered that in PHP, there is a difference between double and single quotes. For example, the two variables below actually behave slightly differently:

$var1 = 'string\t1';
$var2 = "string\t2";

echo $var1; would produce stringt1, whereas
echo $var2; produces string 2 — with a tab character between the ‘g’ and the ‘2’.

Taking things further, the code below:

$myvar = 'text';
echo 'variable: $myvar';
echo "\n";
echo "variable: $myvar";

would output the following:

variable: $myvar
variable: text

So it seems that single quotes will output their contents literally, but double quotes are further processed before being outputted.