Instead of acting on items when the logfile is being read, they act on individual lines in the output. In fact, there are several differences, resulting from the different times at which the aliases are processed. There are lots of implementations of regular expressions. The ones which analog uses are Perl-syntax regular expressions. In general, these are a superset of the extended regular expressions used by Unix egrep or GNU grep -E .
Regular expressions match if they match just part of the string.