Multiple page form with interdependencies?

<?php
if(!function_exists("beforeParseFunction")){
  //Display different form depending on session
  function beforeParseFunction( &$fields, &$templates ){
    global $_lang;
    //which form should we load?
    // $step is set in beforeMailSentFunction or comes from the hidden field
    // we need to do both so that when we step back (eg. the back button of the browser)
    // we still get the proper form
    if(isset($_SESSION['formStep']))
      $step = $_SESSION['formStep'];
    else
      $step = isset($_POST['formStep'])?$_POST['formStep']:1;
    //Kill the session var as otherwise we can't go back to a previous step at all
    unset($_SESSION['formStep']);
    $tpl = $templates['tpl'];
    // Replace form template when needed
    switch($step){
    case 1: //form not yet posted so use tpl as set in snippet call
      return true;
    case 2:
		//build 2nd form using a snippet      
		$tmp = $modx->runSnippet('makeSecondForm',array('age'=>$fields['age'], 'gender'=>$fields['gender']) );
		$tpl = ($tmp) ? $_lang['ef_no_doc'] . " 'second Form'";
      break;
    case 3:
      if( $tmp=efLoadTemplate('multiForm3') ) $tpl=$tmp; else $tpl = $_lang['ef_no_doc'] . " '$replaceTpl'";
      break;
    default: //should never get here
      return false;
    }
     //restore template in array
    $templates['tpl']=$tpl;
    return true;
  }
}
?>

<?php
echo <<<END
<!-- Categories chunk -->
<h3>Starting: step 2 of 3</h3>
<p class="error">[+validationmessage+]</p> 
<form method="post" action="[~[*id*]~]" id="contact">
  <fieldset>
    <input type="hidden" name="formid" value="contact" />
    <input type="hidden" name="formStep" value="2" />
    <p><select name="onderdeel">
			<option value="0">Selecteer onderdeel</option>
			<option value="193693">HD6</option>
                        <option value="193691">DD5</option>
		</select>
</p>
    <input type="submit" name="go"  value="Next" /></p>
  </fieldset>
</form>
END;
?>

<?php
if(!function_exists("beforeParseFunction")){
  //Display different form depending on session
  function beforeParseFunction( &$fields, &$templates ){
    global $_lang;
    //which form should we load?
    // $step is set in beforeMailSentFunction or comes from the hidden field
    // we need to do both so that when we step back (eg. the back button of the browser)
    // we still get the proper form
    if(isset($_SESSION['formStep']))
      $step = $_SESSION['formStep'];
    else
      $step = isset($_POST['formStep'])?$_POST['formStep']:1;
    //Kill the session var as otherwise we can't go back to a previous step at all
    unset($_SESSION['formStep']);
    $tpl = $templates['tpl'];
    // Replace form template when needed
    switch($step){
    case 1: //form not yet posted so use tpl as set in snippet call
      return true;
    case 2:
		//build 2nd form using a snippet      
		$tmp = $modx->runSnippet('eFormCategories',array('age'=>$fields['age'], 'gender'=>$fields['gender']) );
		$tpl = ($tmp) ? $_lang['ef_no_doc'] . " 'FormTwo'";
      break;
    case 3:
      if( $tmp=efLoadTemplate('FormThree') ) $tpl=$tmp; else $tpl = $_lang['ef_no_doc'] . " '$replaceTpl'";
      break;
    default: //should never get here
      return false;
    }
     //restore template in array
    $templates['tpl']=$tpl;
    return true;
  }
}

if(!function_exists("beforeMailSentFunction")){
  //store results in session and advance form
  function beforeMailSentFunction(&$fields){
    global $modx;
    $step = isset($fields['formStep'])?$fields['formStep']:1;
    switch($step){
    case 1: //save values in session
      $_SESSION['age']= $fields['age'];
      $_SESSION['gender']= $fields['gender'];
      $_SESSION['formStep'] = 2; //prepare next step
      break;
    case 2: //save values in session
      $_SESSION['address']= $fields['address'];
      $_SESSION['town']= $fields['town'];
      $_SESSION['formStep'] = 3; //prepare next step
    break;
    case 3://last form
      //from here we go to the report so we need to restore previous values
      // into the fields array so they can be used in the report
      $fields['age'] = $_SESSION['age'];
      $fields['gender'] = $_SESSION['gender'];
      $fields['address'] = $_SESSION['address'];
      $fields['town'] = $_SESSION['town'];
      return true; //return now and let eForm do it's thing
    default: //should never get here
      return false;
    }
    // except for the last step we clear the $_POST array
    // and bypass eform and re-open the page with the next form
    unset($_POST);
    $modx->sendForward($modx->documentIdentifier);
    return false; //
  }
}
//return from snippet
return "";
?>

<?php
$output =  <<<END
<!-- Categories chunk -->
<h3>Starting: step 2 of 3</h3>
<p class="error">[+validationmessage+]</p> 
<form method="post" action="[~[*id*]~]" id="contact">
  <fieldset>
    <input type="hidden" name="formid" value="contact" />
    <input type="hidden" name="formStep" value="2" />
    <p><select name="onderdeel">
			<option value="0">Selecteer onderdeel</option>
			<option value="193693">HD6</option>
                        <option value="193691">DD5</option>
		</select>
</p>
    <input type="submit" name="go"  value="Next" /></p>
  </fieldset>
</form>
END;

return $output;
?>

$tpl = ($tmp) ? $_lang['ef_no_doc'] . " 'FormTwo'";

$tpl = ($tmp) ? $tmp : $_lang['ef_no_doc'] . " 'FormTwo'";