destination-string

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

    Destination string into which STR$LEFT copies the substring.
    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 from which STR$LEFT extracts the substring that it
    copies into the destination string. The source-string argument is
    the address of a descriptor pointing to the source string.

 end-position

    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       read only
    mechanism:    by reference

    Relative position in the source string at which the substring
    ends. The end-position argument is the address of a signed
    longword containing the ending position.

    STR$LEFT copies all characters in the source string from position
    1 (the leftmost position) to the position number specified in
    this end-position argument.