/// <summary>
        /// Finds all matches from any of the provided string keys.
        /// </summary>
        /// <param name="stringKeys">set of string keys to find in index</param>
        /// <param name="errors">Place to add error messages</param>
        /// <returns>match set</returns>
        public MatchSet Matches(List <string> stringKeys, List <string> errors = null)
        {
            MatchSet matches = new MatchSet();

            foreach (string v in stringKeys)
            {
                matches.Or(tIndex[v]);
            }

            return(matches);
        }
        /// <summary>
        /// Finds all matches from any of the provided number keys.
        /// </summary>
        /// <param name="numberKeys">set of number keys to find in index</param>
        /// <param name="errors">Place to add error messages</param>
        /// <returns>match set</returns>
        public IMatchSet Matches(List <UInt64> numberKeys, List <string> errors = null)
        {
            MatchSet matches = new MatchSet();

            foreach (UInt64 v in numberKeys)
            {
                matches.Or(nIndex[v]);
            }

            return(matches);
        }