destination-string

    OpenVMS usage:char_string
    type:         character string
    access:       write only
    mechanism:    by descriptor

    Destination string into which STR$COPY_DX writes the source
    string. Depending on the class of the destination string, the
    following actions occur:

    Descriptor
    Class          Action

    S, Z, SD, A,   Copy the source string. If needed, fill space or
    NCA            truncate on the right.
    D              If the area specified by the destination
                   descriptor is large enough to contain the source
                   string, copy the source string and set the new
                   length in the destination descriptor. If the area
                   specified is not large enough, return the previous
                   space allocation (if any) and then dynamically
                   allocate the amount of space needed. Copy the
                   source string and set the new length and address
                   in the destination descriptor.
    VS             Copy the source string to the destination string
                   up to the limit of the descriptor's MAXSTRLEN
                   field with no padding. Adjust the string's current
                   length (CURLEN) field to the actual number of
                   bytes copied.

    The destination-string argument is the address of a descriptor
    pointing to the destination string.

 source-string

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor

    Source string that STR$COPY_DX copies into the destination
    string; the descriptor class of the source string can be
    unspecified, fixed length, dynamic length, scalar decimal,
    array, noncontiguous array, or varying length. The source-string
    argument is the address of a descriptor pointing to this source
    string. (See the description of LIB$ANALYZE_SDESC for possible
    restrictions.)