The Find First Character in a Set of Characters routine searches
    a string, comparing each character to the characters in a
    specified set of characters. The string is searched character
    by character, from left to right. STR$FIND_FIRST_IN_SET returns
    the position of the first character in the string that matches
    any of the characters in the selected set of characters.

    Format

      STR$FIND_FIRST_IN_SET  source-string ,set-of-characters

1  –  Returns

    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       write only
    mechanism:    by value

    Position in source-string where the first match is found; zero if
    no match is found.

    On Alpha systems, if the relative position of the substring can
    exceed 2**32-1, assign the return value to a quadword to ensure
    that you retrieve the correct relative position.

2  –  Arguments

 source-string

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

    String that STR$FIND_FIRST_IN_SET compares to the set of
    characters, looking for the first match. The source-string
    argument is the address of a descriptor pointing to the character
    string.

 set-of-characters

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

    Set of characters that STR$FIND_FIRST_IN_SET is searching for
    in the string. The source-string argument is the address of a
    descriptor pointing to the set of characters.