6.2.5 Grouping with ()s
Sometimes, within regular expressions, we want to group things together.
Doing this allows building of larger regular expressions based on smaller
()'s are used for grouping.
For example, if we want to match any string that contains
def, zero or more times, surrounded by a
xx on either side,
we could write the regular expression
* character to everything that is in the parentheses.
Thus we can match any strings such as