This value corresponds to the font height in Western scripts,
but is independent of the writing direction (see
FontRequest::IsVertical below). That
means, the value specified here is always measured orthogonal
to the text advancement (height for horizontal writing, and
width for vertical writing).
When this value is negative, its absolute value is taken as
the character size of the font. If this value is positive,
it's taken as the cell size of the font.
This member and the referenceAdvancement member are mutually
exclusive, one of them has to be set to 0 (which means don't
care).
For distorted fonts, the render transformation must be
used. That is, the size specified here corresponds to device
pixel only if the combined render transformation during text
output equals the identity transform. This also applies to all
query methods, for both XCanvasFont and
XTextLayout.
This value specifies the size of the font in the writing
direction (i.e. width for horizontal writing, and height for
vertical writing).
It is equivalent to the referenceCharSize of the FontMetrics
structure.
This member and the cellSize member are mutually exclusive,
one of them has to be set to 0 (which means don't care). For
distorted fonts, the font matrix must be used.
This member supplements the
FontInfo::UnicodeRange0 entry with a specific
locale; this is e.g. important when selecting between
traditional and simplified chinese is necessary (since the
letters have the same unicode ranges and character values).
