The height of this text span, as a multiple of the font size.
When height is null or omitted, the line height will be determined
by the font's metrics directly, which may differ from the fontSize.
When height is non-null, the line height of the span of text will be a
multiple of fontSize and be exactly
fontSize * height logical pixels
For most fonts, setting height to 1.0 is not the same as omitting or
setting height to null because the fontSize sets the height of the EM-square,
which is different than the font provided metrics for line height. The
following diagram illustrates the difference between the font-metrics
defined line height and the line height produced with
(which forms the upper and lower edges of the EM-square):
Examples of the resulting line heights from different values of
See StrutStyle for further control of line height at the paragraph level.
final double height