question: public ZoneRulesBuilder addWindow ( ZoneOffset standardOffset , LocalDateTime until , TimeDefinition untilDefinition ) { Objects . requireNonNull ( standardOffset , "standardOffset" ) ; Objects . requireNonNull ( until , "until" ) ; Objects . requireNonNull ( untilDefinition , "untilDefinition" ) ; TZWindow window = new TZWindow ( standardOffset , until , untilDefinition ) ; if ( windowList . size ( ) > 0 ) { TZWindow previous = windowList . get ( windowList . size ( ) - 1 ) ; window . validateWindowOrder ( previous ) ; } windowList . add ( window ) ; return this ; }
target:  Adds a window to the builder that can be used to filter a set of rules. <p> This method defines and adds a window to the zone where the standard offset is specified. The window limits the effect of subsequent additions of transition rules or fixed savings. If neither rules or fixed savings are added to the window then the window will default to no savings. <p> Each window must be added sequentially, as the start instant of the window is derived from the until instant of the previous window.