Combining Objects into Blocks - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 312

FiGuRE 7.4 The back door opening when the hinge point is picked as the
insertion point
The Delete option erases the selected objects after the block defini-
tion is created, requiring you to insert the block into the drawing.
The Convert To Block option replaces objects with a block definition
as soon as the block is created. In this situation, the Convert To Block
option would be a better choice, but it's a good idea to get some prac-
tice using the INSERT command, so click Delete.
9. Enter a description of the block in the Description field and make sure
Inches or Millimeters is specified in the Block Unit drop-down list,
depending on the units you are using.
The Block Definition dialog box should look similar to Figure 7.5.
10. At the bottom of the dialog box, be sure the Open In Block Editor check
box is selected, and then click OK to close the dialog box.
The Block Editor loads, displaying the A-DOOR-36IN block you just
created (see Figure 7.6).
Because the objects, in this case the door and swing, used to create
the A-DOOR-36IN block were drawn on the A-DOOR layer, the objects
within the block are also on that layer. As discussed earlier, the pre-
ferred practice is to define blocks such as this one on layer 0 so it's
easier to manage.