During initial linking (adding of tabs), the active variable in the tab's isolate scope tracks the active tab. When the first tab is added, it's active is set to true since there's no way to know if subsequent tabs are active since they haven't been added yet. As such, at this point, it is not meaningful to set assign the activeAttrExp with the value of active. At least not until all the tabs have been added. Hence, a good time would be to wait until the next $digest cycle.