I'm not trying to make a line break in the output seen in the browser by the user. I know all about <br> tags and HTML in general. My question wasn't as clear as needed, perhaps.
I'm just trying to put a carriage return (line break) in the HTML code itself so it's easier to read. So, for instance, instead of:
<li>Item</li><li>Item</li><li>Item</li><li>Item</li><li>Item</li>
The PHP would write out the code this way:
<li>Item</li>
<li>Item</li>
<li>Item</li>
<li>Item</li>
<li>Item</li>
Incidentally - the first response answered half my question - that is what the difference in \r and \n is. The question remains, though, do I need all of them?
Does the Mac, Linux, Windows element related to the platform I'm developing on? The web server that PHP is running on? The end users web browser platform? What?
Either way - it doesn't seem to make sense 'cause I've used all three options separately and had them all work just fine on my local Mac that I'm developing and testing on. Questions, questions.