You filter for short texts and message numbers to search for particular messages of a message class. This functionality helps you to find and reuse messages which already exist. So you can prevent creating the almost identical message several times.
You want to check if there are messages which contain the combination 'airline carrier' in the short text. After you have entered this combination in the filter text field, the editor will automatically display the corresponding messages.
After entering the filter text the editor will automatically display the reduced set of messages.