[KevinH]

No, it is a loading progress bar. You can generally only see it work when loading a huge xhtml file (think an entire ebook in one xhtml). For most normal xhtml files it goes so fast you do not see it work. But when people load larger files they need feedback on Previews progress just like a browser would have.

That toolbar is specific to the Preview Dock widget and not to Sigil in general.

How are those icons any different than the buttons and check boxes and things in other dockwidgets like F&R, or the BookBrowser? Or any other button in any of the dialogs? They take up very little room and are typically only used for very specific puposes in that DockWidget where menu's are not typically used.