code: public void updateExpression(String expr, Object value, PageContext pageContext)
              throws ExpressionUpdateException, JspException
      {
          if (isExpression(expr)) {
  
              VariableResolver vr = ImplicitObjectUtil.getUpdateVariableResolver(pageContext.getRequest(), pageContext.getResponse(), false);
              ExpressionEvaluatorFactory.getInstance().update(expr, value, vr, false);
          }
          else {
              String s = Bundle.getString("Tags_BindingUpdateExpressionError", new Object[]{expr});
              _tag.registerTagError(s, null);
          }
      }
docs: This method will update the object identified by the <code>expr</code> parameter with
  the value.  If the
  @param expr
  @param value
  @throws org.apache.beehive.netui.script.ExpressionUpdateException