The subTreeExpiry parameter is ignored when eZFS or eZFS2 handlers are in use.
It is therefore not possible to create cache-blocks with working subTreeExpiry in PHP at this stage.

*eZTemplateCacheBlock::handle()* contains the following check:

if ( $cacheHandler instanceof eZDBFileHandler or $cacheHandler instanceof eZDFSFileHandler )
{
    $subtreeExpiry = eZTemplateCacheBlock::getSubtreeModification( $nodeID );
}

which shows subTreeExpiry only being used for eZDB and eZDBFS handlers.

Changing this code by removing the conditional around it results in the subTreeExpiry working correctly for eZFS.

Since *eZTemplateCacheBlock::getSubtreeModification()* exits immediately if $nodeID isn't set (i.e. subTreeExpiry not used), this fix should have no adverse results.

Steps to reproduce

Use the following code to create a cache-block with subTreeExpiry.

*eZTemplateCacheBlock*

list($handler, $data) = eZTemplateCacheBlock::retrieve( array( 'my_cool_key', $id, ), $nodeID, null );

     if ( !$data instanceof eZClusterFileFailure )
     {
         echo $data;
     }
     else
     {
         // ... generate the data
         $data = '...';
         $handler->storeCache( array( 'scope'      => 'template-block',
                                      'binarydata' => $data ) );
     }

Result: Updating child object of $nodeID does not trigger cache expiry.

Expected result: Updating child object of $nodeID triggers cache expiry.