As you saw in the previous lessons, all the quantifiers including the star *, plus +, repetition {m,n} and the question mark ? can all be used within the capture group patterns. This is the only way to apply quantifiers on sequences of characters instead of the individual characters themselves.

For example, if I knew that a phone number may or may not contain an area code, the right pattern would test for the existence of the whole group of digits (\d{3})? and not the individual characters themselves (which would be wrong).

Depending on the regular expression engine you are using, you can also use non-capturing groups which will allow you to match the group but not have it show up in the results.

Below are a couple different common display resolutions, try to capture the width and height of each display.