Choose this icon to find text in selected subtitles. When you click on this icon, dialog box opens where you type the text you want to find. You can search Up or Down in subtitles and you can specify whether you want to Match Case. When you search for text and you're already on line that contains the text, the searching will begin only on next line (so if subtitles contain no more searched text, you'll end up with message Subtitles don't contain searched text).