title: Spl, ArrayObject, ArrayObject::STD_PROP_LIST
body: <p>I'm trying to understand STD_PROP_LIST constant in the documentation but so far i didn´t understand it, and didn´t found any explanation :(
  The documentation has the following example:</p>
  
  <pre><code>$a = new ArrayObject(array(), ArrayObject::STD_PROP_LIST);
  $a['arr'] = 'array data';                             
  $a-&gt;prop = 'prop data';                               
  $b = new ArrayObject();                                   
  $b['arr'] = 'array data';                             
  $b-&gt;prop = 'prop data';                               
  
  // ArrayObject Object                                     
  // (                                                      
  //      [prop] =&gt; prop data                               
  // )                                                      
  print_r($a);                                              
  
  // ArrayObject Object                                     
  // (                                                      
  //      [arr] =&gt; array data                               
  // )                                                      
  print_r($b);
  </code></pre>
  
  <p>Both prints give me the same exact result:</p>
  
  <pre><code>ArrayObject Object ( [prop] =&gt; prop data [storage:ArrayObject:private] =&gt; Array ( [arr] =&gt;      array data ) ) 
  ArrayObject Object ( [prop] =&gt; prop data [storage:ArrayObject:private] =&gt; Array ( [arr] =&gt; array data ) )
  </code></pre>
  
  <p>Anyone could help me understanding what is the difference between using this constant or not?</p>
  
  <p>Thanks in advance!</p>