KERML_ — Root namespaces restricted to one single file

Usecase: large corporation is working on a project, where also other suppliers deliver parts of the product architecture.

To avoid naming collisions in such constellations, it makes sense to use hierarchical package structures. If everyone just uses plain structures, we have potential conflicts with a duplicate declaration of namespaces.
As within large corporations hundreds of engineers can be working of one product class, which might be organized as namespaces, it makes sense to split the definition of multiple namespaces within the same parent namespace in different files to avoid merge conflicts

Example

package Vehicle{
   part engine : MyCorp::Automotive::Engine::SmallEngine;
   part gearFront : MyCorp::Automotive::Transmission::AT8Gear;
   part rearGear : SomeSupplier::Transmission::FancyGear;
}

Possible resolutions:
1) allow duplicate definitions of namespaces and implicitly merges the resulting trees, dangerous as it could happen unintended
2) allow to merge sub-trees of duplicate namespaces with a keyword
2a) all except one namespace declaration require an addendum keyword, injection of elements possible which might expose private information
2b) all namespaces must declare, that extension is possible

example

partial package CommonParent //declaration can be skipped, if nothing except namespace is declared
package CommonParent::GroupA{
  //some declarations
}
package CommonParent::GroupB{
  //some more declarations
}
package CommonParent::IntegrationLayer{} //should work as no explicitly declared namespace is duplicated
package CommonParent::GroupA::Backdoor {} //should generate an error as the explicitly declared namespace GroupA is duplicated