Layout modifier that tracks focus in the tiled layer while the floating layer or another sublayout is in use. This is particularly helpful for tiled layouts where the focus determines what is visible. It can also be used to improve the behaviour of a child layout that has not been given the focused window.

The relevant bugs are Issue 4 and 306: http://code.google.com/p/xmonad/issues/detail?id=4, http://code.google.com/p/xmonad/issues/detail?id=306

Apply to your layout in a config like:

main = xmonad (def{
                  layoutHook = trackFloating (useTransientFor
                      (noBorders Full ||| Tall 1 0.3 0.5)),
                  ...
              })

useTransientFor and trackFloating can be enabled independently. For example when the floating window sets WM_TRANSIENT_FOR, such as libreoffice's file->preferences window, optionA will have the last-focused window magnified while optionB will result magnify the window that opened the preferences window regardless of which tiled window was focused before.

import XMonad.Layout.Magnifier
import XMonad.Layout.TrackFloating

underlyingLayout = magnifier (Tall 1 0.3 0.5)

optionA = trackFloating underlyingLayout
optionB = trackFloating (useTransientFor underlyingLayout)

It also corrects focus issues for full-like layouts inside other layout modifiers:

import XMonad.Layout.IM
import XMonad.Layout.Tabbed
import XMonad.Layout.TrackFloating
import XMonad.Layout.Reflect

gimpLayout = withIM 0.11 (Role "gimp-toolbox") $ reflectHoriz
      $ withIM 0.15 (Role "gimp-dock") (trackFloating simpleTabbed)

Interactions with some layout modifiers (ex. decorations, minimizing) are unknown but likely unpleasant.