I belive every sitebuilder already had the need to wrap multiple fields with some markup, for example to group them in a fieldset or simply to wrap them with a div to solve theming issues. The easiest way to acoplish that is to use the field group module, wich gives you a nice and handy ui integrated in the core field_ui. It comes with a common set of often used wrappers, like expandable fieldsets or even horizontal and vertical tabs.
The module itself is a great tool for sitebuilders and themers because it is easy to use and exportable with the features module.
Sadly the module is pretty old and it is very complicated to get new features in it, because so many sites already use the module. So everyone lived with the overload of classes field_group appends to its containers and the poor set of available markup. Yannickoo from Loom created a patch, wich allows the user to decide how the wrapper should look like, by simply adding the tag in the ui.
This looks somewhat like in the image above!
If you want to take advantage of this new feature, you need to download the latest development snapshot 7.x-1.x, instead of the stable release.
Credits are going to yannickoo for this great work!