set_thumbnail_yalign

Sets the vertical alignment of the thumbnail for this.

If the page is so tall that [class@TabOverview] can't display it completely and has to crop it, vertical alignment will determine which part of the page will be visible.

For example, 0.5 means the center of the page will be visible, 0 means the top edge will be visible and 1 means the bottom edge will be visible.

The default vertical alignment is 0.

Parameters:

this	a tab page
yalign	the new value