Manual browser: filter(1)
filter — Generic UNIX filtering tool
filter is a generic UNIX filtering tool. It reads data from the standard input, creates a temporary file, executes the desired command (with the absolute filename of the temporary file as the last argument), and writes the contents of the file to the standard output.
The name of a command (and optional arguments) must be supplied directly on the command line.
Issues can be listed and reported at http://www.defora.org/os/project/bug_list/253/Editor.