VMS Help DSR, DSR Flags, Control  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The Control flag (.) is placed at the left margin to begin a
    string of DSR commands. When you want a period to be accepted as
    a text character, you do not need to precede it with an Accept
    flag (_) as long as the period is not placed at the left margin.
    If you do need to have a period in the 0 character position
    (and it is not part of a DSR command), you must precede it with
    an Accept flag. Alternatively, you can use two periods at the
    beginning of a line; the effect is the same as if you had used an
    Accept flag.

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