When packing fixed-format, all input records must have the same length, which must be equal to the second argument, if it is specified. When a record length is specified for a variable length file, no input record may be longer than this length. The correct first record for the file is written to the secondary output stream after the entire file has been processed. Ensure that the first record is written correctly. Null input records are discarded.
Output is written to the primary output stream.
One record is written to the secondary output stream when a variable format file is packed, if an explicit record length is not specified and more than one record is written to the primary output stream. The delay is unspecified. It verifies that the sec- ondary input stream is not connected and then commits to level 0. This is likely to happen when the data has random characters, for example in an encrypted file or a module file.