The Ruleset Builder tab contains 3 groups within the Ribbon. Icons within these groups are activated and the tab remains selected, dependant on the current view within Pathway Developer.
If you select this tab then click on a Rule node the ribbon switches to the Home tab. This is because the Ruleset Builder tab has be used in a split screen mode using the Window tab.
Codeset (Also present on the Home tab)
Window. (Also present on the Home tab)