The USROPN keyword causes the file not to be opened at program initialization. This gives the programmer control of the file's first open. The file must be explicitly opened using the OPEN operation in the calculation specifications. This keyword is not valid for input files designated as primary, secondary, table, or record-address files, or for output files conditioned by the 1P (first page) indicator.
The USROPN keyword is required for programmer control of only the first file opening. For example, if a file is opened and later closed by the CLOSE operation, the programmer can reopen the file (using the OPEN operation) without having specified the USROPN keyword on the file description specification.
See also EXTIND(*INUx).