The list of files or subdirectories that must be staged prior
to executing the command line tool.

Return type of each expression must validate as `["null", File, Directory, Dirent, {type: array, items: [File, Directory]}]`.

Each `File` or `Directory` that is returned by an `Expression`
must be added to the designated output directory prior to
executing the tool.

Each `Dirent` record that is listed or returned by an
expression specifies a file to be created or staged in the
designated output directory prior to executing the tool.

`Expressions` may return null, in which case they have no effect.

`Files` or Directories which are listed in the input parameters
and appear in the `InitialWorkDirRequirement` listing must
have their `path` set to their staged location. If the same
`File` or `Directory` appears more than once in the
`InitialWorkDirRequirement` listing, the implementation must
choose exactly one value for `path`; how this value is chosen
is undefined.
