If you are referencing a variable (as conditionvar or in a copyFrom attrribute) you may always reference to a variable of any other templates by using the Dot-Syntax.

Example:

<patTemplate:tmpl name="source">
This template is a dummy template...<br>
<patTemplate:tmpl name="cond" type="condition" conditionvar="source.foo">
    <patTemplate:sub condition="bar">
        Bar has been supplied!<br />
    </patTemplate:sub>
    <patTemplate:sub condition="argh">
        The argh was here!<br />
    </patTemplate:sub>
    <patTemplate:sub condition="__default">
        unknown<br />
    </patTemplate:sub></p><p></patTemplate:tmpl></p><p></patTemplate:tmpl>