From FCKeditor Docs

The Connector Responses

All Connector responses have the same base XML structure, like this:

<?xml version="1.0" encoding="utf-8" ?>
 <Connector resourceType=" RequestedResourceType">
 <CurrentFolder path="CurrentFolderPath" url="CurrentFolderUrl" acl="CompitedACL" />
 <Error number="ErrorNumber" text="CustomErrorMessage" />
 <!-- Here goes all specific command data -->
</Connector>

Some important things must be considered when building the response:

• The response encoding must be set to "text/xml".
• The "Cache-Control" HTTP header must be set to "no-cache". This is needed because the browsers usually cache the requests for XML files and this is not wanted in this case.
• The Path and the URL must always start and finish with a slash (/).