Setting wgSelectCategoryRoot has no Effect

[zhongzhen]

I wanna make a Playground Namespace with Playground Categories.

There for I've created a special categorie "Playground" wich should be the root category for NS_PLAYGROUND My setting of wgSelectCategoryRoot doesnt have any effect, so I've read the Code and found out, that there is no usage of the parameter wgSelectCategoryRoot in SelectCategoryTagCloudFunctions?.php Than I've seen the Code:

$m_allCats = fnSelectCategoryGetAllCategories();

and thats the only thing where categories are grapped from database, for the cloud. There is no fnSelectCategoryGetAllSubCategoriesUnderRoot($wgSelectCategoryRoot[$current_namespace]) or e.g. Is the wgSelectCategoryRoot setting only for normal SelectCategory?-Extension available and not for this one?

Sorry my english is perhaps a little bit roughly