Combining Objects into Blocks - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 321

FiGuRE 7.15 Markers appear at the increments where the door's swing can be adjusted.
FiGuRE 7.16 The dynamic door block with a smaller door and swing
Finding Blocks in a Drawing
You can detect blocks in a drawing in at least three ways: by using grips, by
using the LIST command, and by looking at the Properties palette.
using Grips to Detect a Block
Grips appear on objects that are selected when no command is started. When
an object that isn't a block is selected, grips appear at strategic places such as
endpoints, midpoints, and center points. But if you select a block, by default only
one grip appears, and it's always located at the block's insertion point. Because