$$ in JsonConfEditor

Hi,

What does $$ mean in JsonConfEdtor? I was poking around NLogLoggingConfiguration and I see it being used (E.x.: [JsonConfEditor(Label = "$$NLog_DefaultTargetConfiguration_Label", HelpText = "$$NLog_DefaultTargetConfiguration_HelpText", Hidden = true, ShowWhen = ".parent._children{.key == 'Enabled' && .value == true }", DefaultValue = "(not configured, not enabled)")])

Is there any documentation on this? This is pretty advanced but very useful stuff!!!!!!