0
SECTION
  2
BLOCKS

Beginning of BLOCKS section

  0
BLOCK
  5
<handle>
100
AcDbEntity
  8
<layer>
100
AcDbBlockBegin
  2
<block name>
70
<flag>
10
<X value>
20
<Y value>
30
<Z value>
  3
<block name>
  1
<xref path>

Begins each block entry  
(a block entity definition)

  0
<entity type>
.
. <data>
.

One entry for each entity definition within the block

  0
ENDBLK
  5
<handle>
100
AcDbBlockEnd

End of each block entry
(an endblk entity definition)

  0
ENDSEC

End of BLOCKS section