CharKeyFrame is the base class for only one subclass, DiscreteCharKeyFrame:
<DiscreteCharKeyFrame KeyTime="0:0:10" Value="t" />
<DiscreteCharKeyFrame .../> animates a Char from a previous value to its own at KeyTime.
The time, relative to the animation, that Value will be reached:
A time period specified in hours:minutes:seconds.
Uniform: The Duration will be split evenly among all key frames.
Paced: The Duration will be split among key frames in a way that ensures the speed of the animation remains relatively constant.
A percentage of the total duration.
The Char value destination