Most often, a fence is placed around elements to group them for manipulation, just as the pointer is dragged around elements to select them with the Element Selection tool. However, a fence has two additional grouping capabilities.

It can be used:

• As a void to exclude elements inside (or overlapping) the fence boundary.
• To clip elements that cross the fence boundary, like a cookie cutter, so that only the parts inside the fence boundary (or outside in the case of a void) are subject to manipulation.

Fences can be rectangular (referred to as a fence block), polygonal (non-rectangular, referred to as a fence shape, with as many as 5000 vertices), or circular (referred to as a fence circle). A fence shape can be derived from a previously placed shape element.

Fences are persistent in both 3D and 2D DGN files. You can place a fence, zoom in on the design and the fence will remain when you zoom back out.