Nested instance in resource of submission

Hi,

I'm making my own control, and I want to use submission:

<xf:instance id="resuorce">
    <value>http://example.org</value>
</xf:instance>

<xf:instance id="source">
    <value>name_of_control_contains_get_parameter_to_resource</value>
</xf:instance>

<xf:submission id="my-submission"
                       instance="sub"
                       mediatype="application/xml"
                       method="get"
                       resource="{instance('resource')}/{xxf:instance('fr-form-instance')/*/*[name() = 'what_should_be_there_?']}"
                       replace="instance"
                       serialization="none"
/>

I mean: I want to make submission to address http://example.org/param and "param" is the content of control in my form, which is named "name_of_control_contains_get_parameter_to_resource". I want to provide this information to resource of submission, byt I do not know how can I use one instance in another:

....
resource="{instance('resource')}/{xxf:instance('fr-form-instance')/*/*[name() = '{instance('source')}']}"
...

That solution is not working. I will be gratful if someone show me how to provide to resource of submission information about address in similar way.

regards,
Tom

Simply:

resource="{instance('resource')}/{xxf:instance('fr-form-instance')/*/*[name() = instance('source')]}"

-Erik

Than You!