6  For accessibility, and to give applications
  a few extra milliseconds between when a widget is built and when it
  appears on the screen, the viewport creates (but does not paint)
  widgets for a few hundred pixels before and after the visible widgets.

7  This approach was first made popular by
  Facebook’s React library.

8  In practice, the t value is allowed
  to extend past the 0.0-1.0 range, and does so for some curves. For
  example, the “elastic” curves overshoot briefly in order to represent
  a bouncing effect. The interpolation logic typically can extrapolate
  past the start or end as appropriate. For some types, for example,
  when interpolating colors, the t value is effectively clamped to
  the 0.0-1.0 range.