Ok, let's try this again.
I need to have a custom combo box for a system setting. There are a number of these widgets defined in manager/assets/modext/widgets/core/modx.combo.js. They are mostly extensions of the initial modx-combo widget.
These widgets get loaded up with the relevant data for display in the system settings.
For example, if I do something like this
$MySetting = $modx->newObject('modSystemSetting');
$MySetting->set('key', 'markitup.set');
$MySetting->set('value', 'set1');
$MySetting->set('xtype', 'modx-combo-rte');
$MySetting->set('namespace', 'markitup');
$MySetting->set('area', 'Rich-Text Editor');
$MySetting->save();
// Clear the cache:
$cacheRefreshOptions = array( 'system_settings' => array() );
$modx->cacheManager-> refresh($cacheRefreshOptions);
I'll get a drop-down with the first option of "set1", then with all the RTEs that I have installed.
The question is, how can I create a custom combo box for my own package's settings? Can I just create one in my build somewhere, using the basic modx-combo as the core?