Given a list of files, ensure that each exists.
| Port | Description |
| source.fileset primary | Input fileset. |
| source.in-memory sequence |
| Port | Description |
| result.fileset primary | Output fileset of files that exist in memory or on disk. |
| result.in-memory sequence | |
| report | List of missing files, formatted as <d:error> elements, or an empty d:errors element if nothing is missing. |
| validation-status | Validation status (http://daisy.github.io/pipeline/StatusXML) of the file check. |