In middleman, how do set variables?
I've started experimenting with middleman and ruby.

The sample layout has this string: 

    <body class="<%= page_classes %>

On any given page, how do I set the 'page_class'?

In middleman, how do set variables?
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I've started experimenting with middleman and ruby.

The sample layout has this string: 

    <body class="<%= page_classes %>

On any given page, how do I set the 'page_class'?
