The IDX (Incremental Design Exchange) format is an XML-based messaging format. It is based on the ProSTEP EDMD (ECAD Design and MCAD Design) open schema for the incremental exchange of PCB layout changes between MCAD and ECAD tools. The iViP organization maintains the format and promotes industry adoption (http://www.prostep.org/en/projects/ecadmcad-implementor-forum.html). EDMD IDX captures and tracks only the proposed design changes initiated by the mechanical or electrical users during a collaboration session. A proposal for change is an EDMD IDX file, and a counter proposal is a separate EDMD IDX file.