The WiredTiger documentation has a section with developer docs, that contains information about how schema operations work:
https://github.com/wiredtiger/wiredtiger/blob/develop/src/docs/arch-schema-ops.dox

There were recently changes in WT-3829 and WT-3964 that changed how those schema operations work, and there is future work scheduled in WT-3965.

The documentation should be updated to reflect the current implementation.