We ouput `span.fieldLayout-header` as parent of every form widget label element currently.
Not only is this unnecessary in my opinion:
- an additional DOM element quickly summing up for bigger forms ([[ https://en.wikipedia.beta.wmflabs.org/w/index.php?title=Special:Preferences&ooui=1#mw-prefsection-rc | OOUI Special:Preferences features 202 of them ]]),
- no CSS/theming advantage due to label being a child and not a sibling element of the real form widget
- naming convention is confusing (`-body` being parent to `-header` and `-field`), although we might not touch this in one task. I would go radically further and remove `-body` altogether as well, as we've got `.oo-ui-fieldLayout` as wrapper anyways. Neither currently in demos, nor in Special:Preferences, nor in any of the other code usages there seems to be any body specific rule [[ https://codesearch.wmflabs.org/search/?q=.oo-ui-fieldLayout-body&i=nope&files=&repos= | that seems indispensable ]].
- FieldsetLayout features -header on `legend` element, not on a parent span. So we would unify
It actually makes the styling and custom overrides unnecessary complex.
Things to be careful about in implementation:
- Help PopupButtonWidget alignment and possible overrides/customizations in extensions
- Breakages of current ``.oo-ui-fieldLayout-header` extensions