crs

Usually references the definition of a CRS, as specified in [OGC Topic 2]. Such a CRS definition can be XML encoded using the gml:CoordinateReferenceSystemType in [GML 3.1]. For well known references, it is not required that a CRS definition exist at the location the URI points to. If no anyURI value is included, the applicable CRS must be either:
a)	Specified outside the bounding box, but inside a data structure that includes this bounding box, as specified for a specific OWS use of this bounding box type.
b)	Fixed and specified in the Implementation Specification for a specific OWS use of the bounding box type.