This is a so called 'regular expression' (RegEx).
Just have a look at this :
http://en.wikipedia.org/wiki/Regular_expression[
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Your RegEx will match when:
0 or more whitespaces (\s*)
are followed by
exactly two digits (\d{2})
followed by ':'
followed by 0 or more whitespaces (\s*)
followed by
exactly two digits (\d{2})
The syntax and behaviour of regEx are depending on the underlaying regEx engine. So there are quite big differences in using regEx in Perl, PHP or C#.
So be carefull with examples from other programming languages.