I try to use single quotes as much as possible and I've noticed that I can't use \n in single quotes. I know I can just enter a newline literally by pressing return, but that screws up the indentation of my code.
Is there some ASCII character or something that I can type that will produce newline when I'm using single quotes?
No, because single-quotes even inhibit hex code replacement.
echo 'Hello, world!' . "\xA";