Whether the page needs attention.
class@TabBar will display a line under the tab representing the page if set to TRUE. If the tab is not visible, the corresponding edge of the tab bar will be highlighted.
class@TabOverview will display a dot in the corner of the thumbnail if set to TRUE.
class@TabButton will display a dot if any of the pages that aren't selected have this property set to TRUE.
Builder instance for fluent chaining
Set needsAttention property.