Showing lines before and after a grep match

Today I ran running grep on the output of hg log, but only to realize that I wanted a couple of lines before and after the line which matched as well.

I am sure this is common knowledge, but I did not know how to do it, so am sharing it in the hope that someone finds it useful.

hg log | grep --before-context=2 --after-context=2 username

Running the above showed me changeset number, comments etc for all the mercurial changesets committed by the specified user.