Must attach to the property Width, what I'm doing this:

     <ColumnDefinition Width="{Binding Path=TabPanelWidth, RelativeSource={RelativeSource TemplatedParent}}" />

-

     public float TabPanelWidth
     {
         get {return (float) GetValue (TabPanelWidthProperty);}
         set {SetValue (TabPanelWidthProperty, value);}
     }
     public static readonly DependencyProperty TabPanelWidthProperty = DependencyProperty.Register ("TabPanelWidth", typeof (float), typeof (BivTabControl), new UIPropertyMetadata (null));

But vozmozhnast need to set not only fixed values, but still a value of type: Auto, 0.5 *, and the like. Any ideas?