Q:

HTML line break in PHP string? 

In Wordpress editor, following code is kind of different to me:
case #1
this is a test&nbsp;

case #2
this is a test
&nbsp;

The first case will add a space after the sentence, and the #2 case will leave an empty line under the sentence. 
Now I am writing a PHP that will include html code in a PHP string,
$post_content = "...."

How to distinguish the two cases above in this $post_content variable? 
If I write
$post_content += "this is a test";
$post_content += "&nbsp";

It's the fist case, how to write the #2 case? 

A:

Newlines are represented by "\n":
$post_content += "this is a test\n&nbsp;";

