Shading
The Bar control consists of a number of rows defined with the 
Width property that make the Bar control thicker or thinner.
The color of each single row is defined by the 
Colors property. If not set, each row will be drawn with the color set in the 
Color or 
Foreground-Color properties.
To obtain a 3-D effect, some rows must be drawn with a lighter or a darker color. This property allows you to draw lighter or darker rows, changing their brightness instead of their color definition
Valid values are:
-2   | Very dark, usually black.  | 
-1   | Darker than normal.  | 
0   | Unchanged.  | 
1   | Lighter than normal.  | 
2   | Very light, usually white.  | 
Since this property can be set for each row, a list of values is needed in order to determine the brightness of each row.
When values are enclosed between parentheses, a new list is defined at once. 
 
Example - A typical 3-D Bar control.
screen section. ...   03 screen-1-br-2 Bar      line 5.0      column 12.0      size 46.0 cells       id 2      color white low      width 2      shading (-1, 1)      .  |