"base documents" vs. "basic documents" for commonly referenced sources

As a non-native speaker, I might be mislead here. I tend to prefer base documents because I think base is a better word for something used as a foundation – and basic might translate to simple. However, when searching for both terms, it appears they are used almost interchangeably, and I have a hard time finding out if one of the two is preferred, or maybe just regionally preferred (AE vs BE or the like).

The exact context is a good term for documents like standards or laws used as references or sources for technical specifications. The term references doesn’t seem to be exactly right, because a reference can be anything, and a base/basic document might be a better hint towards the fact that the documents are referenced similar to a tree structure, i.e. the specifications cite a standard, and never the other way round.