Lockdown: Understanding "nil_lockdown_values"...?

Hi All,

I'm having a bit of trouble wrapping my head around
"nil_lockdown_values" in the Lockdown plugin. I'm unfamiliar with how
exactly this works. I'm assuming it is a helper method of sorts, but
I see no definition. Does Rails simply have the ability to nil_
[somerandomliborclass]_values? Would someone mind unconfusing me?
Also, where would I find information about general features of this
nature? It seems that the API reference doesn't cover items like this
-- or at least not directly.