Issue #2318503 by slashrsm: Define basic interfaces.
Issue #2318503 by slashrsm: Fix typos.
Merge branch '8.x-1.x' into 2318503
Issue #2318503 by slashrsm: Extend FormInterface.
Merge branch '8.x-1.x' into 2318503
Issue #2318503 by slashrsm: Add empty functions to prevent fatals.
Merge pull request #9 from slashrsm/2318503

Define basic functions on interfaces