I've been programming in PHP for nearly 10 years, and I would consider myself to be fairly competent with the language. It's funny that some of the simplest things that I would program in PHP I would just accept certain aspects instead of looking further into them. I am talking in particular about single and double quotes. You can use either of these to output lines of code to a browser. You can even use them interchangeably from line to line.
What's the difference between the two? Well, after going through a beginner PHP course I found out that using double quotes PHP will actually output and render PHP variables; whereas, a single quote will only print out the string without rendering PHP.
As an example, the following PHP code:
$name = 'World';
echo "Hello $name";
Will print out: Hello World
Whereas the following code:
$name = 'World';
echo 'Hello $name';
Will print out: Hello $name
It's funny that it took me that long to figure that out. I guess it was just one of those things I didn't pay attention to. Well, now I know :P