Comment 8 for bug 1242666

For group headers, yes, one reasonable design would be the same as standalone labels but bold.

However, a different reasonable design would be using small caps and a different color.

Whatever the design is, the theme designer should be able to change the style of all group headers at once, without affecting standalone labels. This suggests to me that it should be a separate element.

If this was HTML, an intro label would be <p>...</p>, while a group header would be <h2>...</h2>. People sometimes use <p><b>...</b></p> for headings, but that's a bad idea because it's hard to restyle them later.