I created a page and selected the "Full-width Page Template, No Sidebar" option in the Twenty-Twelve Theme. The viewed page has the following body tag:
<body class="page page-id-2 page-template page-template-page-templates page-template-full-width page-template-page-templatesfull-width-php logged-in admin-bar full-width custom-font-enabled single-author customize-support">
I want to create a child theme with a custom full width page, but I am not sure why I would need to include so many similar classes, or what the best practice would be for creating them. Most of them do not appear to actually be used in styling the page. For example, I can't see the use for page-template-page-templatesfull-width-php. Perhaps it is a bug.