Using setPlaceholder is not globally available.

$modx->setPlaceholder("searchResults", $output);

[+searchResults+]

echo "[+searchResults+]"

print $modx->getPlaceholder("searchResults");

[!eventFunctionSnippet!]
[!eForm? &eFormOnBeforeFormParse=`formParseEvent`  &eFormOnBeforeMailSent=`formParseResults` &formid=`HSF` &tpl=`simple_form` &noemail=`0` &debug=`1`!]

<?php
//search-results
function formParseResults( &$fields, &$templates )
{
        global $modx, $vMsg;

       // this should be outputting the search results;
       print ( $modx->getPlaceholder('holidaySearchResults') );
}

function formParseEvent( &$fields, &$templates, $debug=false )
{
	global $modx, $vMsg;
        $debug = false;
	if ($debug == true)
        {
	print '<pre>GET: '. print_r($_GET) . '</pre>';
	print '<pre>POST:'. print_r($_POST) . '</pre>';
	print '<pre>FIELDS: '. print_r($fields) . '</pre>';
	print '<pre>vMsg: '. print_r($vMsg) . '</pre>';
	print '<pre>rMsg: '. print_r($rMsg) . '</pre>';
        print '<p>' . $modx->getPlaceholder('validationmessage') . '</p>';
        }
	
        $output = '';
	$basePath  = $modx->config['base_path'];
	$siteURL	   = $modx->config['site_url'];

	include_once( $basePath .'assets/snippets/curl/holiday.php' );

	$Holiday = new Holiday(&$modx);
        $sarray = $Holiday->processForm();
        $outcome   = $Holiday->build_sql($sarray);
  
       // set the placeholder
       $modx->setPlaceholder('holidaySearchResults', $outcome );

// if I output the placeholder here it works fine... I just can't seem to output anywhere else...

return true;
} // end function
?>

$val = "hello"

/* instead of setPlaceholder() */

$_SESSION['my_variable'] = $val;


/* in the other snippet, in place of getPlaceholder() */

$mySetting = $_SESSION['my_variable'];

$modx->setPlaceholder('myplaceholder', 'mySetting' ); // if you still need to set a placeHolder