Document @pureOrBreakMyCode

In PR 4180 @shicks said "goog.reflect.cache is also obsoleted by @pureOrBreakMyCode, which can now be used instead of special-purpose caching primitive."
I can't find documentation for this annotation anywhere. How are you supposed to use it to replace calls to goog.reflect.cache? Would it be sufficient to add this into the body of `goog.reflect.cache` or a similar method, or would the callers need the annotation?