Code

const float BACKGROUND_STRING_DISTANCE = 15.0f;
void Diagram_DrawBackground(object sender, DiagramEventArgs e)
{
    e.Graphics.DrawString("Hello world!!!!", this._Diagram.Font, new SolidBrush(Color.IndianRed), e.VisibleRect.X + BACKGROUND_STRING_DISTANCE, e.VisibleRect.Y + BACKGROUND_STRING_DISTANCE);
    e.Graphics.DrawRectangle(new Pen(Color.Chartreuse), e.VisibleRect.X, e.VisibleRect.Y, e.VisibleRect.Width, e.VisibleRect.Height);
}