Simply paste the following code into your functions.php file.
function custom_body_class($classes){ if(is_singular()){ $myvar = "myparam"; } else { $myvar = "anotherparam"; } global $post; array_push($classes, $myvar); return $classes; } add_filter('body_class', 'custom_body_class');
Of course, feel free to adapt the code to fit your needs. For example, a great use can be in multi-language sites: The custom parameter can be used to output the current language in the body class.
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