anchor.diff:      (k: v: v.packageName == "cryptpad")
       (throw "cryptpad not found")
       nodePackages
  -    ;
  +  ;
   
     combined = cryptpad.override {
       postInstall = ''
  
positive.code: 
    };
  in
    combined
  
negative.code:     let
        list =
          lib.concatMap
            (name:
              let v = set.${name}; in
              if pred name v then [ v ] else [ ]
            )
            (lib.attrNames set)
        ;
      in
      if list == [ ] then default
      else lib.head list
    ;
  
    # The cryptpad package attribute key changes for each release. Get it out
    # programatically instead.
  