title: What are exactly $request->attributes?
body: <p>I´m very new to <strong>php</strong> and I don´t quite understand how the attributes are saved in <code>$request</code>.</p>
  
  <p>We´re working with a class Controller.php, which contains every function that transfer the data to the html.twig; a class Model.php, which contains every functions with the queries to get the data from the database; and we work with Twig templates for the html part.</p>
  
  <p>I know, that if I want to get the attributes of <code>'user'</code> I have to write:</p>
  
  <p><code>$request-&gt;attributes-&gt;get('user')</code>, because in there there is an array <code>'user'</code> with the parameters <code>'username'</code>, <code>'password'</code> etc.</p>
  
  <p>But how does this attribute <code>'user'</code> (or whatever parameter) get to be in <code>$request</code>? I need to access to more data through the attributes, but first I have to know how they are saved there. </p>
  
  <p>Thanks!</p>