005002

witness{
 📎 5.2 Distinguishing Bits

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001 [Definition:] The second part in the EXI header is the Distinguishing Bits,
002 which is a two bit field of which the first bit contains the value 1 and 
003 the second bit contains the value 0, as follows.

 DistinguishingBits{1 0 } 

004 Unlike the optional EXI cookie that MAY occur to precede this field, the
005 presence of Distinguishing Bits is REQUIRED in the EXI header. It is
006 used to distinguish EXI streams form text XML documents in the absence
007 of an EXI cookie. This two bit sequence is the minimum that suffices to
008 distinguish EXI streams from XML documents since it is the minimum length
009 bit pattern that cannot occur as the first two bits of a well-formed XML
010 document represented in any one of the conventional charaber encodings,
011 such as UTF-8, UTF-16, UTF-32, UCS-2, UCS-4, EBCDIC, ISO 8859, Shift-JIS
012 and EUC, according to XML [XML 1.0] [XML 1.1]. Therefore, XML Processors
013 that do not support EXI are expected to reject an EXI strem as early as 
014 they read and process the first byte from the stream.
015
016 Systems that use EXI streams as well as XML documents can reliably look
017 at the Distinguishing Bits to determine whether to interpret a 
018 particular stream as XML or EXI.

}