[Behavior] _parent [CGM-to-HTML] The viewer shall load the document into the immediate FRAMESET parent of the current frame in which the current picture is displayed. This value is equivalent to "_self" if the current frame has no parent. [CGM-to-CGM] 
The viewer shall load the picture into the immediate FRAMESET parent of the current frame in which the current picture is displayed. This value is equivalent to "_self" if the current frame has no parent.