gtk:alignment-new (xalign yalign xscale yscale)

xalign -- a float with the horizontal alignment of the child widget, from 0.0 (left) to 1.0 (right)
yalign -- a float with the vertical alignment of the child widget, from 0.0 (top) to 1.0 (bottom)
xscale -- a float with the amount that the child widget expands horizontally to fill up unused space, from 0.0 to 1.0, a value of 0.0 indicates that the child widget should never expand, a value of 1.0 indicates that the child widget will expand to fill all of the space allocated for the alignment
yscale -- a float with the amount that the child widget expands vertically to fill up unused space, from 0.0 to 1.0, he values are similar to xscale

The new gtk:alignment widget.

Creates a new alignment. The gtk:alignment-new function has been deprecated since version 3.14 and should not be used in newly written code. Use the gtk:widget alignment and margin properties.