A regular expression is a set of characters and metacharacters that are used to match text in a specified pattern. You can use regular expressions to match a wide range of conditions.
Assume that you would like to create a condition that will match the sources Google or Yahoo, regardless of whether or not Google and Yahoo are capitalized. Regex for this task is: ([Gg]oogle|[Yy]ahoo).
Take a look at the following example:
The above advanced segment will output all the visits sent by Google or Yahoo! with New visits greater than or equal to 1.