Should EntepriseUserExtension not extend UserResource ?

[fnaeem78]

I am new to Scim, so if I ask some noob question, apologize in advance.
Why does EnterpriseUserExtension not extend UserResource ? Its shown as a child on simplecloud.info.

Secondly if I am implementing a ScimServer (listening to updates from some IdP), then how am I supposed to get extensionValues as explained in
https://github.com/pingidentity/scim2/wiki/working-with-scim-resources#obtaining-extension-attributes

The above link seems to be polling the server to get more info, but what if the request is to update an attribute that belongs to the Extension schema across multiple users ?