code: public RangeSet<Double> getContinuousDomain(){
  		Field<?> field = getField();
  
  		if(field instanceof HasContinuousDomain){
  			RangeSet<Double> validRanges = FieldUtil.getValidRanges((Field & HasContinuousDomain)field);
  
  			if(validRanges != null && !validRanges.isEmpty()){
  				return validRanges;
  			}
  		}
  
  		return null;
  	}
docs: <p>
  Returns the domain of valid values for this continuous field.
  If specified, then all input values that are contained in this set shall be considered valid, and all others invalid.
  If not specified, then all input values shall be considered valid.
  </p>
  
  @return A non-empty set, or <code>null</code>.
  
  @see #getOpType()