That reflect the fact that this page is visible or not on the web site.
A click on it should explain why not.

Here is a reflexion :
A toggle button "Work version" that indicates that the work version is deplayed (no other button might be usable)
A toggle/split button "Online version" that indicates that your are diaplying the validated version (that is moreover online) The underlying menu will have : see the online version, remove from site, go to the preceding validated version.