Begins an annotation's appearance: saves the state as SaveState() does, and the paints until the matching EndAnnotation() are the appearance, composited as one group.
void BeginAnnotation(in DisplayAnnotation annotation)
Where the annotation sits, whether it keeps its size and orientation on screen, and how it is composited.
ISO 32000-2 §12.5.5: the paints that follow are already placed on the annotation rectangle (their transforms include the
matrix AA) and clipped to the appearance's bounding box. A backend that honours NoZoom
or NoRotate (§12.5.3) maps default user space to the device differently until
EndAnnotation(): about the rectangle's upper-left corner, without the device transform's scale or rotation. The
appearance is a transparency group composited with Opacity and
BlendMode (§12.5.5, §11.6.6), through the same compositing formulas as
SetCompositing(Double, Double, BlendMode); inside it, paints composite with the alpha constants and blend mode that
SetCompositing(Double, Double, BlendMode) sets, which EndAnnotation() restores with the rest of the state.
Annotations never nest, and a list that holds one starts it with the identity transform (default user space).