Out of the box, Site Studio nodeIds are unique across all websites on a WebCenter Content instance. However, there is a configuration flag to change this. If the WebCenter Content configuration flag SSGenerateUniqueNodeIdsis set to 0 (false), nodeIds will only be unique within each website.
Be careful changing the default value for SSGenerateUniqueNodeIds to be false. It is usually assumed that nodeIds are unique across all websites on a server and many times this is the way the code has been written.
WebCenter Content Server will deny a check-in when the primary file and the alternate file both have the same file extension. This default behavior is to discourage users from checking the same file in for both the primary and the secondary. Why might they do that? Perhaps they don’t know what the fields really mean?
The primary file should be the original asset. The secondary or alternate file is also called the web viewable file. Examples of proper pairings might include:
See the official documentation here:
Other configurations you may find handy: