I just looked at the code of in the Starter theme:
<body>
{{!-- Insert some custom code by Custom HTML tool --}}
{{{@bodyCustomCode}}}
...
...
{{!-- Insert some custom code by Custom HTML tool --}}
{{{@footerCustomCode}}}
</body>
Conclusion: when you add code to the Body (in the HTML Yool) the code is inserted just after the opening tag of the body element and if you add code to the Footer (again in the HTML Tool) the code is inserted just before the closing tag of the body element.
