code: public void setLocalVariable(String name, Element value)
  			throws EvaluationException {
  
  		assert (name != null);
  
  		localVariables.put(name, value);
  	}
docs: Set the local variable to the given value. If the value is null, then the
  corresponding variable will be removed. If there is a global variable of
  the same name, then an EvaluationException will be thrown. This method
  does not allow children of the referenced value to be set.
  
  @param name
  name of the local variable
  @param value
  value to use or null to remove the variable
  @throws EvaluationException
  if there is a global variable with the same name as the local
  variable