From W3C XForms Group Wiki (Public)
Appearance and Metadata Controls
The @appearance attribute can be used on metadata controls, just as it is used on formal controls. In general, the role of @appearance is advisory to the user-agent - it indicates in general the degree to which the control will occupy space within the user-agent flow.
All user-agents should support a minimum of three states for @appearance (full, compact and minimal), though these may have the same presentation. Additionally, a metadata control may also have other terms used for appearance, but these are implementation dependent. This document does not place any requirements upon the specific forms that these appearance modalities indicate, beyond providing a general range or where each may be appropriate.
@appearance="full" - This is typically the most expansive form of the metadata control. In the case of inline controls such as <xforms:label> this will typically manifest as a heading above the control, while in the case of modal or modeless controls, this may appear as a full dialog box, possibly with rich text support. Full help may also appear inline after a control.
@appearance="compact" - This is an intermediate form that balances the need to present the control with screen real estate limitations. Compact labels may actually appear inline with the control in question. This is typically the default setting. Compact help may appear through the use of a special button or icon near the control itself, or may appear in a status field or shoutout box.
@appearance="minimal" - A metadata control set as minimal will take up as little size as possible while still retaining enough of a presence to be accessible. Minimal labels may appear as content within a text field prior to it receiving the input, or may be a tooltip or similar modeless pop-ups.