Hi,
From DXF reference:
Code 70
Block-type flags (bit coded values, may be combined):
1 = This is an anonymous block generated by hatching, associative dimensioning, other internal operations, or an application.
2 = This block has non-constant attribute definitions (this bit is not set if the block has any attribute definitions that are constant, or has no attribute definitions at all).
4 = This block is an external reference (xref).
8 = This block is an xref overlay.
16 = This block is externally dependent.
32 = This is a resolved external reference, or dependent of an external reference (ignored on input).
64 = This definition is a referenced external reference (ignored
on input).
Gaston Nunez