Hello,
You are asking about multiple environments here.
I would say when it comes to the various indicators Gnome is
the best in terms of accessibility.
To navigate over the parts of a gnome desktop you can use
ctrl+alt+tab and ctrl+alt+shift+tab respectivelly.
When you login into gnome session you will land on an empty
workspace with no apps running.
If you try out navigating with ctrl+alt+tab in this state, you
will recognize you can move between top bar and windows.
The top bar with quick settings and indicators is visible all
the time.
In the pannel reported as windows there are all the
application windows. You can switch between individual apps by
pressing alt+tab or alt+shift+tab respectivelly. You can
switch between multiple windows of the current app (e.g.
multiple browser windows) by pressing alt+grave or
alt+shift+grave (the key in a upper row of keys - immediatelly
above the tab key).
When it comes to navigation on the top bar on the Gnome
desktop I think you will recognize it features similar
navigation paradigm to the menu bar known from your Microsoft
Windows machine. You can use left and right arrow keys to
navigate over the available menus. You enter the menu by
pressing the down arrow. In the menu you can usually navigate
with up and down arrow keys. You can expand or collapse
expandable controls or manipulate the sliders with right and
left arrow keys. You can activate items or toggle checkable
items or select radio items by pressing the enter key. You can
toggle the toggle buttons by pressing the space bar key. When
you expand a collapsed control, you can press down arrow to
jump to its first child and then you can continue navigating
with left and right arrow keys.
On the top bar you will find an Activities toggle button,
current application window menu (only applicable to GTK+3
based apps - analogous to F10 menu in Mate and other GTK+2
based environments), accessibility menu and a system menu with
indicators, with logout and shutdown buttons.
Instead of alt+F1 menu known from Gnome 2, Mate and others,
Gnome 3 features so called activities overview. You can get to
this overview either by pressing the super key alone, or
pressing alt+F1 or by going to the top pannel and toggling on
the Activities button there.
When the overview is showing the application windows are all
minimized and a windows pannel displays window chooser. You
can see all the application windows represented as buttons
here. You can press arrow keys to navigate and enter key to
switch to chosen window.
When the overview is showing you can move to even more pannels
by pressing alt+ctrl+tab and alt+ctrl+shift+tab e.g. dock,
Search and Applications as an addition to top bar and windows.
Dock is a row of icons to your favorite apps and running apps.
You can navigate over the icons by pressing up and down arrow
keys. Individual icons do usually have a popup menu you can
inwoke by pressing the applications key (the key to the left
of the right ctrl key on most keyboards). The popup menu
contains some contextual items for example you can open a new
web browser window, create new text document and similar. It's
app specific. Also you can add or remove an app from
favorites. Favorites are the apps displayed first on the dock.
Ordering of these apps is not accessible via keyboard however
they are ordered as you are adding or removing them from the
favorites using app specific context menus so for example if
you do have Web as the first item, you will hit remove from
favorites inside its context menu, then find it again in the
list and add it to favorites it will be added to the end of
the dock. The last item on the dock is a toggle button you can
use to show or hide the applications view.
Applications view is very similar to the dock except you can
use all four arrow keys to navigate over the apps arranged in
a grid. By default frequently used apps are shown with ability
to toggle the view to display all aps on the bottom of this
view. Popup menus can also be inwoked for the individual apps.
Search has a text entry where you can type your search query.
In fact if you don't require ability to edit the content of
this text entry there is no need to navigate to it because you
can just open up activities and start typing the query. You
can search for apps, documents, files and possibly other types
of content this way because individual apps can plugin into
this mechanism.
There are some predefined keyboard shortcuts. You can browse
over the list of keyboard shortcuts somewhere in the Settings
-> Keyboard. Those include for example super+a to jump
directly to the list of applications from anywhere. Or there
is super+m to jump to the notifications also reffered to as
system tray. This is also on the top bar however I think there
is no other way on how to get into notifications besides
pressing super+m keyboard shortcut.
Also there is an usefull wiki page here on the gnome site you
might like to read to find out more gnome features:
https://wiki.gnome.org/Gnome3CheatSheet
I hope you will find this usefull.
I have never used alt+ctrl+esc within Mate and I do also have
mixed results using pannels on Mate desktop. Still I am using
Gnome more it's why I have chosen to describe it in more details
so you can also get some good use of it.
