Source is:
<form method="get">
  <select name="something" multiple size="2">
    <option selected="selected" value="1">One</option>
    <option selected="selected" value="2">Two</option>
    <option value="3">Three</option>
  </select>
  <input type="submit" value="Try it" />
</form>

Expected result: Multiple values for same key, possibly in an array or comma separated string (i would prefer this and more easy to implement in php core i think :).
Current result: In browser address, the values appears, but php does not provides those values.

PHP Version: 5.3.5
Apache version: 2.2.11.0

In the meantime, i made a workaround of the problem
process_browser_params(); must be called in the very beginning of things.
After this, $_NEWREQUEST will containt both get and post parameters.

function process_browser_params()
{
  GLOBAL $_NEWREQUEST;
  $datas = explode('&', file_get_contents("php://input"));
  for($i=0;$i<count($datas);$i++)
  {
    $datas[$i] = explode('=', $datas[$i]);
  }
  unset($data);
  for($i=0;$i<count($datas);$i++)
  {
    if ((count($data)>0) && (array_key_exists($datas[$i][0], $data)))
    {
      $data[$datas[$i][0]] = $data[$datas[$i][0]].",".urldecode($datas[$i][1]);
    } else
    {
     $data[$datas[$i][0]] = urldecode($datas[$i][1]);
    }
  }
  $_NEWREQUEST = $data;
}

Enjoy

That workaround is fine for data sent as application/x-www-form-urlencoded but won't work if the data is sent as multipart/form-data.

This would absolutely shred backward compatibility: there's already a
documented way of accomplishing this with [], and although HTML allows
multiple values regardless of name, PHP doesn't, and this behaviour is
well established.

Closing won't fix.

Could you comment the second suggestion I made?

That is, why is php://input unavailable when data is sent as multipart/form-data?

Why o why ?

We are in 2021 and this is so well known that I bang my head around it and discover that this is just because there is someone who has implemented it as a map and another one who don't dare to modify it in the next version.

Now my form needs to know the server technology before sending multipart post data.

Backward, awkward.

Not surprising that everybody is using Json.