MPEG4 compliance and the Xvid codec

Hi,
I read at quite a few places (besides the XviD FAQ)
that Xvid is an ISO/IEC MPEG4 compliant video codec.

I was just wondering if it would be safe to assume
that any MPEG-4 compliant video decoder would be able
to decode any stream generated by the Xvid encoder.
What I was just wondering was whether Xvid has an 
optional non-compliant mode, in which it would digress
from what the MPEG4 standard specifies (If I am not 
wrong DivX works this way).

regards
Arvind



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