code: @Override
      public IDocumentQuery<T> whereRegex(String fieldName, String pattern) {
          _whereRegex(fieldName, pattern);
          return this;
      }
docs: TBD expr IDocumentQuery<T> IFilterDocumentQueryBase<T, IDocumentQuery<T>>.WhereRegex<TValue>(Expression<Func<T, TValue>> propertySelector, string pattern)