[[!comment format=mdwn
 username="joey"
 subject="""comment 4"""
 date="2015-12-02T17:29:25Z"
 content="""
It should, in theory, be possible to read [[preferred_content]] and learn
how to write such an expression. Of course, it is a limited form of
programming, and so not for everyone. Which is why git-annex ships with
standard expressions to cover as many common cases as we can think of.
"""]]
