How to cycle through groups?

[txtyash]

This must be a problem faced by everyone but I wonder why I'm unable to find anything about the focus issue.

In the mstab layout there's a master side and a slave side.
Let's say we have a Master and 4 slaves in this order:
| M || A | B | C | D |
Now If want to only work with the M & C windows then focusing between M & C is broken. If my current focus is on C & I need to focus on M then I could use this to directly focus on the master window:

    function()
      local master = awful.client.getmaster(awful.screen.focused())
      if master then
        master:emit_signal("request::activate", "client.focus.byidx",
          { raise = true })
      end
    end,

but if I want to focus on the C window again, then I would have to scroll through A & B or go through D at least.
This could be simplified with bindings to change focus between groups.
ex - Mod+s swaps focus between master and slave side
or have different prevent awful.client.focus.byidx(-1) from cycling through the slave side windows and have different bindings to cycle through slave side windows.