1 Scope
This Recommendation | International Standard specifies a set of basic XML Encoding
Rules (BASIC-XER) that may be used to derive a transfer syntax for values of types
defined in Rec. ITU-T X.680 | ISO/IEC 8824‑1 and Rec. ITU-T X.681 | ISO/IEC 8824‑2. This Recommendation | International Standard also specifies a set of Canonical XML
Encoding Rules (CXER) which provide constraints on the basic XML Encoding Rules and
produce a unique encoding for any given ASN.1 value. This Recommendation | International
Standard further specifies a set of extended XML Encoding Rules (EXTENDED-XER) which
adds further encoders options, and also allows the ASN.1 specifier to vary the encoding
that would be produced by BASIC-XER. It is implicit in the specification of these
encoding rules that they are also used for decoding.
The encoding rules specified in this Recommendation | International Standard:
-
– are used at the time of communication;
-
– are intended for use in circumstances where displaying of values and/or processing them using commonly available XML tools (such as browsers) is the major concern in the choice of encoding rules;
-
– allow the extension of an abstract syntax by addition of extra values for all forms of extensibility described in Rec. ITU-T X.680 | ISO/IEC 8824‑1.
This Recommendation | International Standard also specifies the syntax and semantics
of XER encoding instructions, and the rules for their assignment and combination.
XER encoding instructions can be used to control the EXTENDED- XER encoding for specific
ASN.1 types.