VMS Help DIFFERENCES, Qualifiers, /COMMENT_DELIMITER  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /COMMENT_DELIMITER[=(character[,...])]

    Ignores characters on a line to the right of (and including) a
    specified comment character.

    If you specify just one character, you can omit the parentheses.
    Lowercase characters are automatically converted to uppercase
    unless they are enclosed in quotation marks. Nonalphanumeric
    characters (such as ! and ,) must be enclosed in quotation
    marks. Multicharacter comment characters are not allowed. You
    can specify up to 32 comment characters by typing the character
    itself or one of the following keywords. (Keywords can be
    abbreviated provided that the resultant keyword is not ambiguous
    and has at least 2 characters; single letters are treated as
    delimiters.)

    Keyword          Character

    COLON            Colon (:)
    COMMA            Comma (,)
    EXCLAMATION      Exclamation point (!)
    FORM_FEED        Form feed
    LEFT             Left bracket ([)
    RIGHT            Right bracket (])
    SEMI_COLON       Semicolon (;)
    SLASH            Slash (/)
    SPACE            Space
    TAB              Tab

    If you specify the /COMMENT_DELIMITER qualifier, the
    /IGNORE=COMMENTS qualifier is implicitly also included.

    If both the uppercase and lowercase forms of a letter are to be
    used as comment characters, the letter must be specified twice,
    once in uppercase and once in lowercase. If you do not include
    either a comment character or a keyword with the /COMMENT_
    DELIMITER qualifier, the DIFFERENCES command assumes a default
    comment character based on the file type. For some file types
    (.COB and .FOR), the default comment characters are considered
    valid delimiters only if they appear in the first column of a
    line.

    The following characters are the default comment delimiters for
    files with the specified file types:

    File Type        Default Comment Character

    .B2S, .B32,      !
    .BAS, .BLI
    .CBL, .CMD       ! and ;
    .COB             * or / in the first column
    .COM, .COR       !
    .FOR             ! anywhere and C, D, c, d in the first column
    .HLP             !
    .MAC, .MAR       ;
    .R32, .REQ       !