Is it possible (simpleType or complexType)?

Is it possible to define a schema for this?

I have element <arg>. I want that <arg> has simpletype (xs:integer) or only one child <var> and any other elements or text.
I don't want to create a new element e.g <number> for simpletype

<arg>
12345
</arg>

or

<arg>
    <var/>
</arg/>

please, help mi