Sets the vertical alignment, from 0 (top) to 1 (bottom).
This affects the children allocation during transitions, when they exceed the size of the hugger.
For example, 0.5 means the child will be centered, 0 means it will keep the top side aligned and overflow the bottom side, and 1 means the opposite.
| this |
a hugger |
| yalign |
the new alignment value |