screen commands for switching between regions are: actually focus up, focus down, focus right and focus left. To type these commands (or any other screen command, for that matter) you type C-a :focus up, for example.
These commands are tedious to type, that's why you must create key bindings in your ~/.screenrc file. Since I'm a Vim user I opted for these lines in my ~/.screenrc file:
bind j focus down
bind k focus up
bind l focus right
bind h focus left
To switch to the left region I type C-a h
tmux and screen have different models so there is no exact equivalent.
In screen terms, a split lets you display multiple windows at the same time. next (C-a n) rotates windows through the active part of the split; this lets you rotate “hidden” windows through the active region of the split.
In tmux terms, a split divides a window into one or more panes. Each part of a split window is an individual pane, panes are never hidden (if a window is selected (visible) all its panes are, too), and a pane can only be used in a single split of one window (a pane can not be in multiple windows, and it can not be in multiple splits of the same window). There are commands to move panes around in (or between) windows, but not in an identical way to next in screen.
You could use a binding like the following to arrange a similar effect:
bind-key C-n swap-pane -s :+.top \; rotate-window -Ut :+
You will probably want to put this in your ~/.tmux.conf file, but you can just type/paste it after Prefix : to bind it in your current server instance.
To use the binding, pick your “main window”, split it, create a “pane container” window immediately after the “main window”, then use the binding to rotate any pane in the “main window” among the group in the “pane container” window.
Here is how you might create the setup:
Pick a window to use as your “main window”. Start (e.g.) Vim in it.
Split your “main window” into two panes.
E.g. Prefix " (:split-window)
You can use this pane as your testing window (or log viewer, or whatever).
Create a new window (the “pane container”) immediately after your main window.
E.g. Prefix c (:new-window)
It is important that no other window gets between the indexes of the “main window” and the “pane container” window (+ in the window specifiers used in the bound commands means “the next higher numbered window”).
Split this window into a number of panes. To rotate through three panes, split this window into two panes (the third pane is the one in the “main window”).
Maybe you need a shell for git, and a shell for running a database interface. Put each in a separate pane in this “pane container” window.
Switch back to your “main window”. Select the pane that you want to “rotate out”.
You can use Prefix Up/Down/Left/Right to move among the panes.
Invoke the binding to swap the current pane with the first pane in “pane container” window and (“behind the scenes”) rotate the panes inside the “pane container” window (so that the next time you run the binding, the first command swaps with the “next” pane in the sequence).
Prefix Control-n (the binding use C-n, but you could change this to whatever you like).
To scroll backwards through the panes, you can use the below:
bind-key C-p swap-pane -s :+.bottom \; rotate-window -Dt :+
Best Answer
I looked at the STRING ESCAPES section of the screen man page and found what you may be after. The ? escape is like an if statement and the : escape is like an else statement. The F escape is true when that window has the focus. So the if-then-else statement for the if active then, else would look like this (padding added for readability):
The original option was %{= g} (pad string to display width and green) changing the active screen text to bright red will look like this:
https://www.gnu.org/software/screen/manual/screen.html#String-Escapes