A good feature of Magento’s layout blocks structure is that it gives you the option to dynamically call methods on any given layout block within any layout handle.
I recently came across an instance of where it would of been really convenient to a body class to the whole frontend account area of Magento.
The below code is how I achieved that :
customer-account
To add a body class to any other page using the layout XML, then simply copy the following code into the layout handle you would like it to apply to :
replace-with-your-class