The Whole Word option is provided for when a substring search would give too many false hits. EG searching for "it" would normally match any word that contained those letters together like "fit" or "pitch". Turning on the Whole Word option allows you to find just the occurrences of the word "it". It works by checking that any match has a non-word character both before and after it. Word characters are defined as: a-z A-Z 0-9 _ and characters 128 through to 254.