Ruby (borrowed from Perl and common in many regex impls I believe) has the "x" modifier to ignore whitespace and comments in literal regexes, for example:

    str = "2012-10-04T07:20:00"

    str =~ /
        (\d{4}) # four digit year
        -
        (\d{2}) # two digit month
        -
        (\d{2}) # two digit day
        T
        (\d{2}) # two digit hour
        :
        (\d{2}) # two digit min
        :
        (\d{2}) # two digit sec
       /x