The TFileOpen structure.

 // FileOpenRead, FileOpenWrite, FileOpenAppend, FileOpenWriteLinear,
 // FileOpenWriteNonLinear, FileOpenReadLinear
 TFileOpen    struct
  Result      word    // The function call result.
  FileHandle  byte    // The returned file handle to use for subsequent file operations.
  Filename    byte[]  // The name of the file to open or create.
  Length      dword   // The desired maximum file capacity or the returned available length in the file.
 TFileOpen    ends

Possible Result values include Loader module error codes.