What do the $form in the code say?

The following code in the $form one will declare this one will be assigned value that, it is a mess, I do not know how these logically in the way?

function __tostring () {$form = "; return $form;}

Reply to discussion (solution)

The appended assignment is followed.

The ultimate purpose of this function is to construct the contents of the variable of the form, the content of which is HTML

$form This is a variable, do not be confused because the variable is called form, and the next. = In fact is $form = $form + "..." The meaning

If $form.= '';
Then equivalent to $form.= $form + '';
My doubts are '' Well understood, but what is the equivalent of $form?

$form = "Hello";
$form. = "World";
Echo $form;
Output
Hello World

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