Great news!
I'll wait for the next release then.
Thank you for all your work on this project!

Cheers,

Olivier

I misunderstood your original request. I thought you wanted to create 
nested task lists (task lists under other tasklists).

What you are describing here is actually already supported in the 
ActiveSync library, but you need support for it in the applications 
too - and this support is already implemented in Nag 4.2 (and likewise 
in Kronolith 4.2, Turba 4.2, and Mnemo 4.2) by enabling the "Support 
separate collections" preference in each app.

Ah, I see. Well, I don't know if Windows Phone supports this feature, 
but BlackBerry 10 does.

Here is the part of the synclog asking for the folder to be created. 
IT seems like 3 commands need to be implemented, create, delete and 
change.

2013-11-22T11:49:22+01:00 INFO: [] Maximum memory usage for ActiveSync 
request: 5700952 bytes.
2013-11-22T11:49:22+01:00 INFO: [93417] 
Horde_Core_ActiveSync_Driver::authenticate() attempt for user@domain
2013-11-22T11:49:23+01:00 INFO: [] FOLDERCREATE request received for 
user user@domain
2013-11-22T11:49:23+01:00 INFO: [93417] Device entry exists for 
BBMYPIN, updating userAgent and version.
2013-11-22T11:49:23+01:00 INFO: [93417] Request being handled for 
device: BBMYPIN, Supporting protocol version: 14.1, Using 
Horde_ActiveSync v2.9.0
2013-11-22T11:49:23+01:00 INFO: [BBMYPIN] Handling 
FOLDER[CREATE|DELETE|CHANGE] command.
2013-11-22T11:49:23+01:00 DEBUG: [93417] I  <FolderHierarchy:FolderCreate>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   <FolderHierarchy:SyncKey>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I     
{528a9d45-01f4-4a15-ab90-1d8e4e2e3851}1
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   </FolderHierarchy:SyncKey>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   <FolderHierarchy:ParentId>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I     @Tasks@
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   </FolderHierarchy:ParentId>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   <FolderHierarchy:DisplayName>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I     Secret
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   </FolderHierarchy:DisplayName>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   <FolderHierarchy:Type>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I     15
2013-11-22T11:49:23+01:00 DEBUG: [93417] I   </FolderHierarchy:Type>
2013-11-22T11:49:23+01:00 DEBUG: [93417] I  </FolderHierarchy:FolderCreate>
2013-11-22T11:49:23+01:00 INFO: [93417] Loading state for synckey 
{528a9d45-01f4-4a15-ab90-1d8e4e2e3851}1
2013-11-22T11:49:23+01:00 INFO: [93417] Loading FOLDERSYNC state 
containing 6 folders.
2013-11-22T11:49:23+01:00 INFO: [93417] 
Horde_ActiveSync_Connector_Importer::importFolderChange(, Secret, 
@Tasks@, 15)
2013-11-22T11:49:23+01:00 ERR: Creating sub collection not supported 
in the @Tasks@ collection.

The primary reason this is not supported is because I don't have any 
clients that support this. What client are you using that is able to 
create the sub folders? Can you send me a synclog of your attempt to 
do this so I can see how it is sent?

Using outlook.com as a backend, it's possible to create task groups 
(sub collection) from mobile devices.
It's quite useful to be able to group task per project per examples.

When a mobile device using Horde as a backend creates such folders, 
Horde fails with an error 500.

Here is what's in the logs
2013-11-21T18:38:38+01:00 ERR: HORDE [horde] Buffer contents:  [pid 
61910 on line 162 of "/usr/local/lib/php/Horde/Rpc/ActiveSync.php"]
2013-11-21T18:38:40+01:00 ERR: HORDE [horde] Returning HTTP 500 while 
handling FolderCreate command. [pid 63816 on line 156 of 
"/var/www/html/webmail/rpc.php"]
2013-11-21T18:38:40+01:00 ERR: HORDE [horde] Error in communicating 
with ActiveSync server: Creating sub collection not supported in the 
@Tasks@ collection. [pid 63816 on line 162 of 
"/usr/local/lib/php/Horde/Rpc/ActiveSync.php"]
2013-11-21T18:38:40+01:00 ERR: HORDE [horde] #0 
/usr/local/lib/php/Horde/ActiveSync/Connector/Importer.php(336): 
Horde_Core_ActiveSync_Driver->changeFolder(false, 'Secret', '@Tasks@', 
false, '15')
#1 /usr/local/lib/php/Horde/ActiveSync/Request/FolderCreate.php(148): 
Horde_ActiveSync_Connector_Importer->importFolderChange(false, 
'Secret', '@Tasks@', '15')
#2 /usr/local/lib/php/Horde/ActiveSync/Request/Base.php(249): 
Horde_ActiveSync_Request_FolderCreate->_handle()
#3 /usr/local/lib/php/Horde/ActiveSync.php(881): 
Horde_ActiveSync_Request_Base->handle()
#4 /usr/local/lib/php/Horde/Rpc/ActiveSync.php(143): 
Horde_ActiveSync->handleRequest('FolderCreate', 'BBMYPIN')
#5 /var/www/html/webmail/rpc.php(156): Horde_Rpc_ActiveSync->getResponse(NULL)
#6 {main} [pid 63816 on line 162 of 
"/usr/local/lib/php/Horde/Rpc/ActiveSync.php"]
2013-11-21T18:38:40+01:00 ERR: HORDE [horde] Buffer contents:  [pid 
63816 on line 162 of "/usr/local/lib/php/Horde/Rpc/ActiveSync.php"]