We should declare all our public errors here

No good declaring it internally if it is publicly accessable

I cant spot anywhere where we would want users to provide one of these, and don't want to encourage it

core.go is ambiguous with the newer types added to the package, and this file will get hard to read once documention expands the line count

Having moved the DB interface out, this name makes sense

This function is unlikely to be implemented for quite a while and as it modifies an existing collection, it comes with a load of synchronization questions that should be answered properly before we can assume it will exist in the currently declared form

Note: this function is untested