Temporarily yanks the focused window out of the layout to mostly fill the screen.

You can use this module with the following in your xmonad.hs:

import XMonad.Layout.Maximize

Then edit your layoutHook by adding the Maximize layout modifier:

myLayout = maximize (Tall 1 (3/100) (1/2)) ||| Full ||| etc..)
main = xmonad def { layoutHook = myLayout }

Or, if you want to control the amount of padding placed around the maximized window:

myLayout = maximizeWithPadding 10 (Tall 1 (3/100) (1/2)) ||| Full ||| etc..)
main = xmonad def { layoutHook = myLayout }

For more detailed instructions on editing the layoutHook see the tutorial and XMonad.Doc.Extending.

In the key-bindings, do something like:

       , ((modm, xK_backslash), withFocused (sendMessage . maximizeRestore))
       ...

For detailed instruction on editing the key binding see:

the tutorial.