Yii2：视图中的全局变量

I'm need to concatenate lines for later output (markdown processing...). This is why I use a function l() and a global variable $content.

My view code:

$content = "";
function l($line="") {
    global $content;
    $content .= $line."
";
}
l("hello");
echo "+";
echo $content;
echo "-";

outputs

+-

I'd expect:

+Hello-

Why? What am I doing wrong?

I am using PHP 7.2.6

EDIT:

There are several PHP related answers as this one. But they don't help. I suppose the problem is related to Yii2 and more specific to Yii2 view handling.

Found the solution! Crazy!

Yii2 renders the view inside an object instance.

This means, the PHP variable declaration

$content = "";

is not global but local to the rendering context.

The solution for question is to make the variable declaration in the view global, too:

global $content = "";

The working code inside the view looks like this now:

global $content = "";
function l($line="") {
    global $content;
    $content .= $line."
";
}
l("hello");
echo "+";
echo $content;
echo "-";

Bingo!