I can't say what may happen on any webpage, but when it comes to Windows, groups as part of the ribbon interface all behave in the same way, regardless of the program involved. I wrote the following tutorial a couple of years ago:
The tutorial I put together was done very quickly, and like so many things under Windows, there is more than one way to achieve the same ends, and the same keystrokes will behave according to the context in which they are invoked.
When you hit ALT, and only ALT, to throw focus to the collection of Ribbon Identifier Tabs at the top of a program, at that time, the left/right arrows will move you from ID tab to ID tab, announcing the ribbon that you have focus on, but you are not yet in the controls for that ribbon, you are only on its identifier tab.
When sitting on an identifier tab for a ribbon, hitting either TAB or Down Arrow will throw focus on the leftmost control in the leftmost Group (essentially, first control of the first control Group) in the ribbon. At this point is when the functionality of the arrow keys changes, and things can get messy, which is why I prefer TAB for control by control traversal within a group and moving between all the groups (if that’s what you’re looking to do). Using TAB will go, control by control, through a group before moving to the next group. CTRL+L/R Arrow will jump directly from the group you’re currently sitting in to the previous/next group in the ribbon. The CTRL+L/R Arrow gives you a way to traverse groups quickly whether you’re exploring them, or you know, say, you want a control in the Paragraph group in Word. It’s much quicker, once you’ve dropped into the Word ribbon’s clipboard group (leftmost), to hit CTRL+R Arrow 2 times to jump to the paragraph group and start looking than it is to hit TAB 21 times to get through each and every control in the Clipboard and Font Groups before arriving at the first control of the Paragraph Group. Were you to use the L/R and Up/Dn Arrow keys once you’ve dropped into the ribbon, they behave very much like they do were you navigating a table, and where Groups are ignored as far as how navigation behaves. For example. If you drop yourself into the Word Home Ribbon and start navigating with TAB, you’ll start on the Paste split-button control in the Clipboard Group, then land on the Cut, Copy, Format Painter, and Office Clipboard control for the Group (the last one). If you continue tabbing you go into the Font group, through all its controls one by one, then the Paragraph and its controls one by one, etc. If you drop yourself into that same Ribbon, but use R arrow as your navigation key, you do start on the Paste split button, but move to the right to copy, then to the right again, into the Paragraph group to the Bold, Italic, Underline split button, strikethrough, subscript, superscript, then, finally, clear formatting controls. If you keep R-Arrowing you then move in to the Paragraph Group to the left justify, center, right justify, even distribution justify, then line and paragraph spacing control. Essentially, you’ve run across the ribbon Groups, through the center of each, hitting only the controls in the middle of each. There are controls both above and below the center line in each of the groups, and using the other arrow keys would move you in the respective directions. This can be very handy once you already intimately know the controls in a group and you want to get to one you know is, say, below the bold control (which happens to be the Text Effects and Typography control). For myself, I never use the straight L/R/Up/Dn arrow keys for navigating the ribbon. I far prefer sticking to CTRL+L/R arrow to move between Groups, and TAB to move between controls in a Group so I know I’ve hit all of them.
As to your question about using Dn Arrow rather than 4 TABs in File Explorer, sure, you can think of that as a shortcut if you like. But it’s really just an artifact of the way File Explorer is designed. There are a couple of controls in the File Explorer frame that most of us, including me, never use, and using TAB will land on those first before dropping into the actual ribbon controls while hitting Dn Arrow bypasses those and drops you straight in to the Ribbon controls.
As I’ve said repeatedly, and it applies generically, any OS is wildly complex, and the exact details of how a given keystroke will behave is very specific to context. The same keystrokes get used over and over again, and those for specific function (e.g. CTRL+S) tend to remain static across programs while things like the arrow keys, tabbing, etc., change up a bit depending on what needs to be traversed in context, which changes depending on the Window in use. You can safely presume they’ll move you, but exactly how and exactly where is entirely dependent on the Window you have open and the program that’s running in it, be it File Explorer, MS-Word, some music composition program, etc., etc., etc.
As to substituting “horizontal arrows” for L/R Arrow and “vertical arrows” for Up/Dn Arrow this falls into a “that ship has sailed” category. The actual directional indicators (whether fully written out or abbreviated) are a part of the culture of computing, and not limited to assistive technology. While I can go for the logical shortening of left and right as L/R, and up and down as Up/Dn, that’s the extent I can go for (or at least that I think would be accepted and communicate precisely).
Q: So, if I understand your explanation, tab/shift+tab move among all
A: Correct. Though I prefer to think about CTRL+arrow key as moving between ribbon groups. It’s got to land somewhere when landing in a group, and that somewhere is on the first control for the group it’s landing in. Groups themselves are just containers for their controls, so you can’t land on a group, just in one.
Q: But you're saying that they (TAB/SHIFT+TAB navigation) cycle through all groups, which implies that I could theoretically tab from the first to the last control in the entire ribbon menu.
A: Correct, and not “theoretically,” as that’s precisely what happens. When you jump from the last control in a given group to the first control in the next the Group name is announced as part of that jump so you know you’ve exited one group and entered another. It's conceptually the same as a menu in the sense that you land in a menu but then you begin navigating its controls. The menu itself is the container, but the menu itself serves no other function.
I would not use your terminology about zoom in/out with regard to navigation keys. The CTRL+Arrow navigation is group navigation, or group-to-group navigation. TAB navigation (or SHIFT+TAB) I simply next/previous for whatever the context happens to be, whether in ribbons, webpages, or whatnot. In the case of ribbons, it’s next/previous control, except when on the very first or very last control at which point wrapping back/forward occurs, which is pretty typical overall.
There are, and always have been, controls outside the ribbon, and when they are present they rest on “the window frame” very much like the minimize, maximize, and close controls always do. It’s just that most of us never touch them. But like all things, a screen reader cannot presume to know whether you actually want to use, for example, the Save, Undo Split Button, Redo/Repeat typing button, or Customize Quick Access Toolbar control that are part of the window frame for MS-Word. So it’s got to visit them, and when it visits them is as part of the “ribbon go round.” There are a couple of other controls, too, related to your account if you’re using one of the newer versions of Office as well as the Ribbon Display Options button.
With regard to sliders, the original physical slider on audio control equipment (with which I am quite certain you must be familiar) is used to increase (up) and decrease (down) some attribute. On things like mixing boards, these are always oriented vertically, but I’ve seen some older stereo equipment where they were oriented horizontally. When oriented horizontally (left/right) going to the right always increases and left always decreases. It makes conceptual sense to always use the up/down arrow keys for increase/decrease independent of how a given designer may have chosen to orient the actual display of a slider.-----
Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
A gentleman is one who never hurts anyone's feelings unintentionally.
~ Oscar Wilde