the horizontal alignment of the child widget, from 0 (left) to 1
(right).
yalign
the vertical alignment of the child widget, from 0 (top) to 1
(bottom).
xscale
the amount that the child widget expands horizontally to fill up
unused space, from 0 to 1.
A value of 0 indicates that the child widget should never expand.
A value of 1 indicates that the child widget will expand to fill all of the
space allocated for the GtkAlignment.
yscale
the amount that the child widget expands vertically to fill up
unused space, from 0 to 1. The values are similar to xscale.