How to specify in a XML schema that 2 attributes can't be present at the same time?

Question

Anyone knows how to prevent a XML to have 2 attributes at the same time?

I have an XML which gives information about liquid containers:

What I want

Example 1:

<container>
  <bottle volume=1/>
</container>

Example 2:

<container>
  <bottle size="small"/>
</container>

Example 3:

<container>
  <bottle/>
</container>

I use 2 different attributes to indicate the quantity of liquid a container can contain but I don't want to have the possibility to indicate twice the same information by putting both attributes at the same time:

What I don't want

<container>
  <bottle volume=1 size="small"/>
</container>

Anyone knows how to forbid that?

EDIT: I must use XSD 1.0

Answer 1

It can't be done in XSD 1.0.

It's easily done in XSD 1.1 using assertions (or type alternatives).

The traditional way to do this without XSD 1.1 is to use Schematron for a second validation pass.