This repository hosts a copy of the OGC schemas available from http://schemas.opengis.net as well as an excerpt of the W3 schemas from http://www.w3.org.
Additionally there are proposed changes as well as extensions to those XML schemas available.
These extensions include work in progress that are currently discussed in the relevant working groups of the OGC mainly the WCS.SWG and might change without notice. There is no guarantee whatsoever that these proposals will get officially adopted by OGC.
More information about EOxServer is available at http://eoxserver.org.