Gets or sets the em size used for rendering the Glyphs.
A value that represents the em size used for rendering.
This property is read/write. The default value is 0.
Em size is a typographical measure that specifies the approximate width of the capital letter "M" in the Roman alphabet, measured in the units that are prevalent in a particular technology. Silverlight em sizes are given in pixels. The apparent visual size of the em size varies per font.
Note that the default FontRenderingEmSize is 0. Therefore, in order to render anything with Glyphs, you should specify a FontRenderingEmSize either in XAML or script. This is in contrast to TextBlock, in which font sizing defaults to 14.666 (pixels).