public void FindNext(DocumentPosition fromPosition)
{
            ...
            DocumentTextSearch textSearch;
            if (this.matchCaseFlag)
            {
                this.options = RegexOptions.None;
                textSearch = new DocumentTextSearch(this.Document, this.options);
            }
            else
            {
                textSearch = new DocumentTextSearch(this.Document);
            }

            TextRange find;
            if (this.matchWholeWordsOnlyFlag)
            {
                var wholeWordSearchText = string.Format("\\b{0}\\b", this.GetSearchText());

                find = textSearch.Find(wholeWordSearchText, fromPosition);
            }
            else
            {
                find = textSearch.Find(this.GetSearchText(), fromPosition);
            }
            ...
}