2.5.2.1 APPEND Command
  The APPEND command merges a BASIC source program
  with the program currently in memory. The program in
  memory must be a BASIC source program that has been
  placed in memory with the OLD command or entered in the
  environment. The program must also contain at least one
  line number.

  If both programs contain a line with the same number, the
  appended program line replaces the current program line.

  If you type APPEND without specifying a file name, BASIC
  prompts with:
  Append file name--

  You should respond with a file name. If you respond by
  pressing Return, VAX BASIC searches for a file called
  NONAME with the default file type of .BAS. If the compiler
  cannot find the file, it signals an error.

  The APPEND command does not change the name of the
  program in memory.