Regular Expressions - Some examples

As part of one investigation, i had go do some experiments with the regular expressions and below is some findings on it.

^(?:(4|3|2|1)(\\.[0-9]{0,2}\\.[0-9]{0,2})|(?:(5)\\.[0-9]\\.[0-9]{0,2}))$

The above expression will check and make sure the version from 1 - 5 versions, and each version can be of format x.xx.xx 

the above expression will return true for 5.0.xx - 5.9.xx But not anything on and above 5.10.xx 

2. Now lets say, the rule #1 applies but as a special case, we want to introduce a scenario where we need to get TRUE for 6.1.3 , this is possible by modifying reg-ex like below 

^(?:(6.1.3))|(?:(4|3|2|1)(\.[0-9]{0,2}\.[0-9]{0,2})|(?:(5)\.[0-9]\.[0-9]{0,2}))$

References:

http://www.perlmonks.org/?node_id=1094450

http://www.regular-expressions.info/tutorial.html