Calling macro with tricky parameter name

Hello all,

I have a macro that I want to use for producing html5 page (fragments). 
It looks like this:

<#macro input id params...>
<#list params?keys as param>
     Key: ${param}<br />
     Value: ${params[param]}<br />
</#list>
</#macro>

Question: How do I call that macro with parameter named data-custom with 
the value freemarker?

The naive aproach would have been:

<@input id="something" data-custom="freemarker" />

Background:
In html5 they have the new convention that you can enter custom data 
attributes  on elements by using a data- prefix on all attributes. I 
suspect that my question is likely to reoccur in the future as html5 
becomes more common.

I've browsed through the FAQ and .vars in mentioned for accessing the 
variables but that isn't a problem me (since I'm iterating through params).

Is there a way to specify a tricky parameter name somehow?

Thanks in advance!

//Jerker


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