Jumping into multiple file systems.
The most direct way is to use git to add folders of files. Your document environment is the files you clone to your repo.
But a more advanced use would want to be able to override parts of that. That overriding could be done in parallel to the way we handle overriding of key/values. As each key/value in a file has higher priority than key/values in referenced files, so a reference to a file should be satisfied from the local file system, but if not found, then can be obtained from a referenced file system. So, one could have a small file system of one's own stuff, and reference another file system as something like:

• CmA_=[http://commonaccord.org/Doc/]

This would have the effect of including all the CommonAccord files with a prefix of CmA_.