type property Null safety
The type of scroll this is (e.g. line, page, etc.).
This indicates the intent of the scroll, not necessarily the size. Not all scrollable areas will have the concept of a "line" or "page", but they can respond to the different standard key bindings that cause scrolling, which are bound to keys that people use to indicate a "line" scroll (e.g. control-arrowDown keys) or a "page" scroll (e.g. pageDown key). It is recommended that at least the relative magnitudes of the scrolls match expectations.
final ScrollIncrementType type;