code: int intersectionWithEnvelope2D(Envelope2D clipEnv2D,
  			boolean includeEnvBoundary, double[] segParams,
  			double[] envelopeDistances) {
  		Point2D p1 = getStartXY();
  		Point2D p2 = getEndXY();
  
  		// includeEnvBoundary xxx ???
  
  		int modified = clipEnv2D.clipLine(p1, p2, 0, segParams,
  				envelopeDistances);
  		return modified != 0 ? 2 : 0;
  
  	}
docs: inside clipEnv2D.