How to change the clip of an XGraphics

Hi, 

I don't know whether I can ask this question here or not but I still wonder if someone could help me.

I'm a little confused about setting clipping area of an XGraphics, pdfSharp only provide a method IntersectClip, which means if I want to change the clipping area, the area would become smaller and smaller(intersect with the previous area), does anybody know that is there anyway to set the clipping area freely?

Regards,

Edgar