The rules by which the PM implements clipping are as follows:

• Any primitive completely outside the clipping boundary is discarded.

  When a primitive crosses a clipping boundary, any part outside the boundary is discarded.

• Any primitive completely within the clipping boundary is retained.

  When a primitive crosses a clipping boundary, any part within the boundary is retained.

• When the clipping boundary is a clip path, viewing window, or graphics field, any point that falls on the boundary is considered within the clipping boundary.

  When the clipping boundary is a clipping region, any point on the top or right boundaries of a rectangle is discarded; and any point on the bottom or left boundaries of a rectangle, that is not on the right or top boundaries also, is included in the region.