NOT opened by `open SheetDescription` - it has to be asked for. `==>` is already Fable.Core.JsInterop's object-literal operator (used in FilesIO, MainView and TruthTableView) and FsCheck's implication operator. Opening this module alongside either of those shadows one with the other, silently, by order of the open statements. So open it only in a file that uses neither - which is all of the test files. `connect` above is the same function and carries no such hazard.