How can we show the standard and custom error messages at same time?

Hi All,

How can we show the standard and custom error messages at same time?

Is there any method to show the standard error message and custom error message at the same time?

Here is the scenario is that it is a form to fill in information, and also attachment. Some of the essential information and attachment are required to fill in. If I input none of the field and attachment, it will only show the standard error message first. Only when I input all the field with standard error message, and if keep the attachment field is blank, then the custom error message finally shows. So I want that the both these error message are shown simultaneously.

Please give suggestion