controlCurve must contain a gml:Curve element
gml:Curve must have "srsName" attribute set
At least one segment must be a gml:Bezier, gml:LineStringSegment, gml:GeodesicString.
No other segments allowed besides gml:Bezier, gml:LineStringSegment, gml:GeodesicString.
Degree of the Bezier must be "3"
Beziers must have exactly two knots
The value of the first knot must be 1.0
The value of the second knot must be 2.0
Multiplicity of each must be degree+1 (=4)
Weight of each knot must be 1.0