The StageScaleMode class provides values for the Stage.scaleMode property.
Stage.scaleMode
inline read onlyEXACT_FIT:StageScaleMode = 0
inline read onlyNO_BORDER:StageScaleMode = 1
inline read onlyNO_SCALE:StageScaleMode = 2
inline read onlySHOW_ALL:StageScaleMode = 3