[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2015-10-06T19:01:13Z"
 content="""
This should be easy enough to implement; just implement a property that
ensures the file lacks an authorized key (probably using `File.lacksLine`)
and then combine the two properties with `<!>` to get a RevertableProperty.

I'd accept a patch that does that.
"""]]
