X83 is a GAEB DA 2000 XML / GAEB DA XML file, used by the GAEB standard.
GAEB is the German Joint Committee on Construction Electronics and promotes the use of computers in construction. DA stands for Datanaustausch Aufbau which roughly translates to construction data-exchange.
This file lists building specifications and “dv-technical schema XML” technical information, meant to be exchanged between those involved in a construction project. The X83 is the request for proposal within the formal specification/