The frequency or interval settings control how often a lightbox, or stateful action, is shown to a user through the use of a cookie. The cookie is based on a lightbox identifier number between 0 and 31 and their display frequency interval that is set through a selector. When you set both inputs, they distinguish this experience's lightbox (or action) from any other lightboxes (or action) using the same ID. This gives you total control over the frequency at which a lightbox is shown to a particular visitor or segment.
Currently, lightboxes and statefulBanners both use this file to record their state. This means you cannot show a statefulBanner and a lightbox with the same ID together. Therefore, you must select an option from Display Frequency.
Every Page
Lightboxes that display on every page don't require any cookie to control frequency. The frequency is "always show," as long as action conditions and WHO targets allows this action to fire.
Once per Session
The cookie name for the lightbox state is mt.s-lbx. It expires at the end of a session (s = session).
mc.lightboxState.SESSION_COOKIE = 'mt.s-lbx';
Once, Ever
The cookie name for this lightbox state is mt.i-lbx. It never expires (i = infinite), although the actual value is 10 years. A lightbox set to Once, Ever only uses the mt.i-lbx infinite cookie to ensure that it won't appear again and flip the mc.lightboxState.lightboxShown flag to tell Monetate's lightbox ops that the customer has seen this lightbox previously and should not be shown it again.
mc.lightboxState.INFINITE_COOKIE = 'mt.i-lbx';
Once Every X Days
The cookie name for this lightbox state is mt.c-lbx. It expires in X number of days (c = custom).
mc.lightboxState.CUSTOM_COOKIE = 'mt.c-lbx';