The Efficient XML Interchange Working Group has published a Proposed Edited Recommendation of Efficient XML Interchange (EXI) Format 1.0 (Second Edition). This document is the specification of the Efficient XML Interchange (EXI) format. EXI is a very compact representation for the Extensible Markup Language (XML) Information Set that is intended to simultaneously optimize performance and the utilization of computational resources. The EXI format uses a hybrid approach drawn from the information and formal language theories, plus practical techniques verified by measurements, for entropy encoding XML information. Using a relatively simple algorithm, which is amenable to fast and compact implementation, and a small set of datatype representations, it reliably produces efficient encodings of XML event streams. The grammar production system and format definition of EXI are presented. Comments are welcome through 20 November. Learn more about the Extensible Markup Language (XML) Activity.