destination-string
    OpenVMS usage:char_string
    type:         character string
    access:       write only
    mechanism:    by descriptor
    Destination string into which STR$REPLACE writes the new string
    created when it replaces the substring. The destination-
    string argument is the address of a descriptor pointing to the
    destination string.
 source-string
    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor
    Source string. The source-string argument is the address of a
    descriptor pointing to the source string.
 start-position
    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       read only
    mechanism:    by reference for CALL entry point, by value for JSB
                  entry point
    Position in the source string at which the substring that
    STR$REPLACE replaces begins. The start-position argument is the
    address of a signed longword containing the starting position.
    The position is relative to the start of the source string.
 end-position
    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       read only
    mechanism:    by reference for CALL entry point, by value for JSB
                  entry point
    Position in the source string at which the substring that
    STR$REPLACE replaces ends. The end-position argument is the
    address of a signed longword containing the ending position.
    The position is relative to the start of the source string.
 replacement-string
    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor
    Replacement string with which STR$REPLACE replaces the substring.
    The replacement-string argument is the address of a descriptor
    pointing to this replacement string. The value of replacement-
    string must be equal to end-position minus start-position.