Good points; I haven't used those much. Not sure if this is a windows vs. mac os convention. Notepad++, Eclipse, and Visual Studio will all unindent with shift-tab at the beginning of a line
I can understand having shift-tab differ depending on context (such as filling in snippet fields), but in plain default mode, I don't think it makes sense to turn off shift-tab=unindent. Why would you want shift-tab to act the same as tab, especially when the unindent command is listed as being bound to shift-tab in the menu?
Is that not a bug, especially when setting