code: public void setExpression(Expression exp)
    {
    	if(null != m_mainExp)
      	exp.exprSetParent(m_mainExp.exprGetParent()); // a bit bogus
      m_mainExp = exp;
    }
docs: Set the raw expression object for this object.
  
  
  @param exp the raw Expression object, which should not normally be null.