Can _param('filename') be set to true?

• Per docs, first argument to _param(), when called from inside

  fill_in(), must be one of the "eight legal options":

     PACKAGE              HASH
     BROKEN               OUTPUT
     BROKEN_ARG           DELIMITERS
     SAFE

• Something's fishy

• Where's the eighth option?

• Turns out it should be:

     PREPEND

• Error not found until 5 months later!