playout:SetLineSpacing(factor)
Typical values are: 0, 1, 1.5, 2. The default values is 0.
If factor is non-zero, lines are placed so that
baseline2 = baseline1 + factor * height2 |
where height2 is the line height of the second line
(as determined by the font(s)). In this case, the spacing
set with playout:SetSpacing() is ignored.
If factor is zero (the default), spacing is applied as before.
Note: for semantics that are closer to the CSS line-height property, use the line height attribute in a Pango attribute list.