The extended (ODS-5) file name syntax offered by Extended File
    Specifications supports a larger character set and relaxes
    restrictions on lengths of file names and use of characters. This
    syntax allows Windows NT-style file names that use the following
    character set and naming conventions to be stored on and accessed
    by OpenVMS systems.

1  –  Character Set Support

    The ISO Latin-1 Multinational character set is a superset
    of the traditional ASCII character set used by versions of
    OpenVMS previous to 7.2. With extended file specifications, all
    characters from the 8-bit ISO Latin-1 Multinational character set
    are valid in file specifications, except the following:

       C0 control codes (0x00 to 0x1F inclusive)
       Double quotation marks (")
       Asterisk (*)
       Backslash (\)
       Colon (:)
       Left angle bracket (<)
       Right angle bracket (>)
       Slash (/)
       Question mark (?)
       Vertical bar (|)

    File specifications on an ODS-5 volume can also include Unicode
    (UCS-2) characters. Because each Unicode character requires
    two bytes, the use of Unicode characters can affect the maximum
    permitted lengths of file specifications.

2  –  Special Characters

    Some ISO Latin-1 characters require the circumflex (^) to precede
    them in a file specification in order to be interpreted as
    literal characters rather than special function characters.
    The circumflex (^) is interpreted by the system as an escape
    character.

    o  The circumflex (^) followed by underscore (_) or by a space
       represents a space.

    o  The circumflex (^) followed by any of the following characters
       means that the character is to be used as part of a file name
       rather than having any special meaning that it might otherwise
       have in a file specification:

       .  ,  ;  [  ]  %  ^  &

    o  A user can enter a literal period (.) with or without the
       circumflex (^) in a file name. The system adds the circumflex
       to any periods other than those that act as delimiters for the
       file type and version number. Literal periods (.) in directory
       names must be preceded by the circumflex.

       File names containing special characters cannot be accessed
       from a VAX system.

3  –  Interpretation of Period

    The introduction of the period (.) as a literal character in
    extended file names requires RMS to determine which periods are
    file name characters and which are delimiters.

    When only one period (.) is used in an extended file name, that
    period is interpreted as the delimiter, as in "Venice.Venezia;1"
    above. As in previous versions of OpenVMS, this behavior also
    occurs if the single period is followed by a number:

    $ CREATE Test.1

    creates the file:

    Test.1;1

    When there are multiple periods (.) in a file name, the system
    looks at all the characters after the last period. If those
    characters are five or fewer digits, or a minus sign (-) followed
    by five or fewer digits, the period is interpreted as a version
    delimiter and the period previous to it is a type delimiter.
    Notice that a legal version is less than or equal to 32767.
    If you try to create the file "grandioso.x.33333", the "33333"
    causes an illegal version error. If there is a nonnumeric
    character following the last period then it is interpreted as
    a type delimiter.

    For example, the following command: $ CREATE Test4.3.2.1

    creates the file: Test4^.3.2;1

    where .2 is the file type and 1 is the file version.