Many parameters of Google Data queries have a restricted set of supported values. The Zend_Gdata_Data class contains constant definitions for all the legal values.

The isValid() static function tests that a value is valid for a specified attribute. The example below shows usage of a constant, and a test of that constant using isValid().

<?php
require_once 'Zend/Gdata/Data.php';
$vis = Zend_Gdata_Data::VIS_PRIVATE;
if (Zend_Gdata_Data::isValid($vis, 'visibility')) {
    ...
}
?>

The getValues() static function returns an array of valid values for a specified attribute.

<?php
$visValueArray = Zend_Gdata_Data::getValues('visibility');
?>