anchor.diff:      elem
       filter
       findFirst
  -    flip
       foldl
       foldl'
       getAttrFromPath
  
positive.code:           [{ inherit (module) file; inherit value; }]
          ) configs;
  
        resultsByName = flip mapAttrs declsByName (name: decls:
          # We're descending into attribute ‘name’.
          let
            loc = prefix ++ [name];
  
negative.code:             in
                throw "The option `${showOption loc}' in `${firstOption._file}' is a prefix of options in `${firstNonOption._file}'."
            else
              mergeModules' loc decls defns) declsByName;
  
        matchedOptions = mapAttrs (n: v: v.matchedOptions) resultsByName;
  
  